In most real estate transactions, the focus is on the purchaser and whether he or she can afford to buy the property. But there is another, equally important question: Can the seller afford to sell?

Many sellers become riveted on the gross selling price, and fail to consider how much money they need to net in order to move to their next residence. And that can be a serious mistake, especially if they haven’t built up much equity in their current homes.

The commission they are paying the listing agent is sometimes overlooked, as is the share of their buyer’s closing costs they’ll be expected to pay, what they owe on their current mortgage, and the costs of the actual move.

If the seller doesn’t take those and other costs into consideration, his or her agent should, says Margaret Rome, the broker-owner at HomeRome Realty in Baltimore. It’s part of the agent’s job.

“What the seller needs has no bearing on the price. It is the place to start the discussion,” Rome posted recently on real estate site ActiveRain. “It is a must to find out (the seller’s) expected dollar amount. If no one has explained the cost of selling, or they don’t understand the fees, even with a full-price offer, (the seller) may not be able to afford to sell.”

Her advice to colleagues: “Never price a home without knowing what is owed and what the owners need to move forward. Find out the bottom line, their in-their-pocket number.”

More than a handful of deals have fallen through because a seller didn’t do the math -- or an agent didn’t urge them to.

“It amazes me how many sellers are surprised by all the additional costs,” said Endre Barath of Berkshire Hathaway Home Services in Beverly Hills, California.

Carol Williams of Wenatchee, Washington, once inherited a listing in which she figured out that if the owners did move forward, “they would probably be left homeless.” The sellers’ credit was in bad shape and they had hardly any equity. Fortunately, at her suggestion, they spoke with a lender and discovered the harsh reality of their situation. “They took the home off the market and stayed put,” she said.

According to a recent analysis from Zillow and Thumbtack, a home improvement marketplace, the typical owner will shell out $20,851, mostly in taxes and commissions, to sell their place.

Here’s a brief rundown of some of the costs of selling:

-- Prep work. Window-washing, painting, landscaping, repairs, staging to make the house more presentable -- none of these will add much, if anything, to your home’s value, but they should help sell the place more quickly.

-- Payoff. If you have a mortgage, you’ll have to pay the balance at closing. But the equity you’ve built up in your home should ease the sting, especially if you’ve owned it for five years or more. Home equity loans and second mortgages also have to be paid off, and your lender may charge a fee to do so.

-- Commission. Typically 5% or 6% of the selling price, this amount will be split between your agent and the buyer’s. On a $300,000 selling price, a 5% commission comes out to $15,000. But commissions are totally negotiable.

-- Inspection. It’s smart to get an independent home inspection to find any major issues and get them fixed --before a potential buyer’s inspector finds them and uses them as bargaining tools. Figure on spending $500-$700.

-- Closing costs. Yes, sellers have closing costs. And depending on how strong or slow the market is, the buyers may demand that you also pay some, or all, of theirs. Under this broad heading, there are recording fees, title insurance, warranty, settlement fees, appraisal fees, lawyers’ charges and settlement agent’s fees, along with bills for property taxes, utilities and homeowner’s association dues for the months you lived in the house. Together, these could add up to as much as 10% of the selling price.

-- Repairs. There’s no way to estimate this in advance, but anything your buyer wants fixed means money out of your pocket. Big-ticket items like termite remediation or roof repairs are obviously expensive, but even minor fixes can add up.

-- Moving. You can save beaucoup bucks by “hiring” friends and family help you move (a few six-packs and a couple pizzas should do the trick). Ditto if you rent a van. If you employ professional movers, expect to pay a couple of thousand, easily -- more, if you’re moving across state lines.

-- Utilities. Many power and water companies require new customers to put up a deposit when they open accounts, especially if you are moving to another city or state. You’ll get it back when you move out. But for right now, it’s cash out of your pocket.

-- Travel. Cross this item out if you aren’t moving far. But if you are moving long-distance, figure on racking up some significant dollars for hotels and meals.

Homebuyers who expect their newly built castles to be flawless masterpieces are only fooling themselves: The perfect, zero-defect house has yet to be built.

A house is a giant jigsaw puzzle. Not only does it come in as many as 10,000 pieces -- many of which don’t always fit as precisely as they should -- it is put together by dozens of human beings, sometimes working at cross purposes in harsh, if not extreme, weather conditions, almost always under a fast-approaching deadline.

So, yes, builders make mistakes -- sometimes big ones. Like the house Avex Homes built in the Tampa area that was too close to its neighbor. The county rules say no house should be within 10 feet of another, but Avex crews built one with a gap of less than 6 feet. The builder was required to lop 4 feet off the completed house.

This kind of major snafu is a rare occurrence, to be sure. Even structural defects in which one or more load-bearing elements could suffer a catastrophic failure are few and far between.

According to Paul Thomas, national risk manager at 2-10 Home Buyers Warranty, an average of only 1 percent of all new houses suffer a major structural defect over their first 10 years. Of course, that varies; geographic areas with water intrusion issues or expansive soils tend to have more problems.

Minor issues occur more frequently. About 5 percent of all homes, Thomas reports, experience drywall cracks from foundations settling or wood shrinkage.

Face it: Nails pop out from the drywall as a house settles, concrete is going to crack, doors may not close precisely, a floor tile might crack and a bathtub or sink might have a scratch or two. Annoying, yes, but easily repaired without too much hassle.

But every builder has a whopper of a story about a big mistake. A subcontractor misreads a blueprint, a building inspector fails to catch a major flaw, or a product is totally defective and irreparable. Builders won’t talk about these miscues on the record, lest their names become synonymous with shoddy construction, but they’ll share them anonymously.

Here are some of their taller tales:

-- A building inspector in Coeur d’Alene, Idaho, discovered that a house’s foundation had been poured 6 inches over the property line, largely because there was 4 feet of snow on the ground. The foundation had to be removed and redone. Fortunately, the mistake was discovered before construction got any further. Had the house been built in its entirety, the builder would have had to seek a variance from the city -- an iffy prospect at best.

-- A Maryland builder once left his blueprints at home, and instead of going back to retrieve them, he guessed on the site lines. He guessed wrong, by 2 feet, and had to start over in the right place.

-- In Columbia, South Carolina, a builder poured the concrete slab over the pipes before he called for a plumbing inspection. He had to break up the slab and start all over again. And he said he has recurring nightmares about building the wrong house on the wrong lot -- a mistake he hasn’t made, at least not yet, but that remains his worst nightmare.

-- That nightmare became a reality for a Seattle builder, who was able to persuade his buyer to switch lots. And a Dayton, Ohio, builder who built four houses on the wrong lots is still mired in a court battle while the four houses sit empty.

-- Then there’s the story of the builder who built the garage ordered by one buyer on the house next door. He solved his dilemma by giving the garage to the neighboring house’s buyer free of charge, and building another one on the right house. “There wasn’t anything else I could do,” he told me.

-- Many builders have horror stories about carpentry nails being driven into plumbing pipes. And once those nails start to work themselves loose, the result is often a slow leak, but sometimes a gusher of a flood.

-- A San Antonio builder recalls the time a carpenter put a window in the wrong place. Just before stopping for lunch, he marked the center of where the window should be. But when returned, he used the mark as a corner, throwing the opening off-center by 18 inches. Only when the house was finished was the error discovered: Four windows lined up perfectly, but the fifth one didn’t.

But not all miscues turn out badly. In Boston, for example, a crew put a gable roof on a house that called for a Tudor style. The buyer was the first to notice the mistake; the builder, who thought it looked awful, was sick about it. He said he would remove the roof and replace it with the proper one.

But the buyer liked it just the way it was. So did some others: Of the next four buyers of the same model house, two ordered their homes with gable roofs as well.

At a recent business dinner in New York City, Rosalie Berg said she was wondering what had become of service in the mortgage sector. Seemed like too many loan officers had forgotten what the word meant.

Berg, who runs Stategic Vantage, a housing finance-centric public relations and advertising firm, had cold-called five lenders when she wanted to refinance her South Florida home. She was shocked at the response -- or worse yet, the lack thereof.

Of the five, three never returned her call, and the other two took more than a day to reply.

“People were not very responsive,” Berg told me. “It really surprised me.”

Our dinner host was Sue Woodard, chief customer officer at Total Expert, a marketing and sales software system for lenders. And she had had a similar experience. When she called to close out her equity line of credit, the lender’s representative didn’t ask why; he just said he’d send over the paperwork without any follow-up at all.

That, says Woodard, who has been in the mortgage business for 30 years, was a “big opportunity missed in a very competitive market.”

Worse, perhaps, she says she has a thousand similar stories. Most recently, her lawn service canceled her contract because it wants to focus solely on commercial work. So she called eight other services that do work in her neighborhood. Not one called back.

“I guess the economy is doing too well,” she commented. “No one seems to want more business.”

Also at dinner was Woodard’s colleague at Total Expert, Brett Cadogan, the firm’s director of strategic alliances. He had his own story about a lack of service. He had listed his house for sale with the wife of the guy who was building his new house. But after five months, he cut her loose, along with her builder-husband, calling the whole thing “a terrible experience.”

When he attempted to start the process all over again a few months later, Cadogan called five agents. Two were “very responsive,” he said. But of the other three, one never returned his call and two didn’t get back to him for a week to 10 days.

Noting that listings are “the lifeblood” of realty agents -- “That’s how they get paid,” he said -- he was really surprised by the response rate. “The level of urgency was pretty much nonexistent.”

The fourth at this dinner was yours truly, and boy, did I have a few stories of my own. Most recently, I have been going round and round with a home warranty company I won’t name directly -- it used to have a fellow named Roebuck in its handle -- but with which I will not do business again. Ever!

When our double oven stopped working, I called this company to repair it, not knowing that it no longer has its own crews, but farms the work out. After several attempts to fix my machine, I still don’t have an oven. But finally, some four months later, the warranty company has agreed to replace it. After all the stalling so far, though, I’ll believe it when I see it.

Then there’s my experience with an insurance company in Florida after Hurricane Irma, as well as my dealings with a big-box retailer that sells all kinds of home-related materials. To this day, the insurance company has yet to return my phone calls, even though I explain in my message that I have letters from two different roofers saying that I have enough damage from the big storm to warrant an entirely new roof.

The company has already closed out my claim, something I didn’t think it would until someone called to say they had received some information from one of the aforementioned roofers. They sent out an engineer weeks ago and I have heard nothing since.

I suppose the next step is to call the insurance commissioner in Florida to complain. I am told that insurers don’t want to be on the bad side of the Florida regulator, so we will see.

The big-box store where I bought new flooring was very slow on the uptake -- that is, once it had my money and the floor was installed. I called several times to complain that the installer had used someone else’s materials, even though they were told not to, and that my contractor was back-charging me.

I wanted the store to cover the charge, which was the installer’s fault, not mine. Once I was actually able to talk with a human being, that person said she would get back to me. Two weeks later, nothing. So I called again and spoke with her associate, who told me he would check it out. Two more weeks, and nothing.

Finally, a month or so later, a representative called to say they would be processing my refund. That’s great, but it shouldn’t have taken so long and so many calls. It has left nothing but a bad taste in my mouth, so much so that I don’t think I will ever buy another thing at this chain, even if I have to drive out of my way to go elsewhere.

Spending your money with a competitor is certainly one way to fight back. But it’s better to keep copious notes about your conversations with customer service people, including their names, identification numbers, the date and the time of day. Never, ever be nasty. Always remain calm. You can express your anger or disappointment without cursing or screaming.

If you get no satisfaction, escalate your beef to a supervisor or manager, either on the phone, in writing or directly at the store or office in question. And if that doesn’t work, take your issue higher and higher up the corporate ladder.

Twice I’ve written a letter to the chairman of Comcast, and both times, the response was swift and favorable.