This week, it's time to take on a couple of otherwise sacrosanct real estate homilies: The tax deduction for mortgage interest and the commission realty firms charge to sell houses. None of the professionals who earn their livelihoods in the housing sector will like reading this, but here goes anyway.

First, the write-off for interest borrowers pay on their mortgages: Uncle Sam allows us to deduct every penny we pay in mortgage interest, up to $1 million a year. Of course, few people pay that much, but it is part of the tax code nevertheless.

According to 2014 estimates by the Congressional Joint Committee on Taxation, the mortgage interest deduction accounted for $72.4 billion in savings for taxpayers. About 34.5 million taxpayers claimed the popular write-off.

But most of that money must have gone to better-heeled taxpayers, because at today's still extremely low loan rates, the write-off is all but useless, at least to folks who purchase modest houses.

This all hinges on how much money you borrow and at what interest rate. The more you borrow and the higher the rate, the more attractive the write-off becomes. But at today's low rates, it may be better to claim the standard $12,600 tax write-off that's available to everyone.

To illustrate, let's look at the average median home price of $288,000 for March, as reported by the Census Bureau. With a typical 5 percent down payment ($14,400), you'd borrow $273,600. And at an interest rate of, say, 4 percent, the monthly payment for principal and interest on a 30-year loan would be $1,306 and change.

In the first year of the loan, you'd pay $10,1856 in interest, so it would be better to claim the standard $12,600 deduction for a couple filing jointly than to itemize.

It's not until the amount borrowed in the above example is somewhere between $317,000 and $318,000 that the better choice is to itemize.

The numbers change as interest rates and borrowed amounts change, but you get the idea. If you expect a big tax break when you are buying your first house, you'd better do the arithmetic ahead of time. Otherwise, you could be in for a shock.

You can find calculators to help with the math all over the internet. I use the calculators at HSH Associates (www.hsh.com), a highly respected mortgage information service based in New Jersey.

Also, it doesn't matter whether you buy a new or an existing house; the calculation is the same. The only thing that may change the equation is your property taxes, which are also deductible.

According to the Joint Committee, 33.6 million taxpayers claimed the property tax deduction, to the tune of $30.2 billion in 2014.

If you want to claim your real estate taxes, you should itemize. Often, the two deductions -- mortgage interest and property taxes -- add up to more than the standard deduction.

And there are many other write-offs -- state income taxes, medical payments, office in the home -- that, all added up, also favor itemizing.

Renters also qualify for the standard deduction, even though they have no mortgage interest or property taxes. But they may have other write-offs that are more than the standard deduction. Most do not, though, which is why renters rarely itemize.

Now, on to real estate commissions: In reality, commissions are always negotiable. But finding a brokerage firm or agent willing to bargain on their fees is all but impossible. There are discount brokerages that charge based on the services they provide, but full-service firms? Forget about it!

At the same time, the brokerage business's main trade group is always trying to get someone else to cut their fees. Just a few weeks ago, Tom Salomone, president of the National Association of Realtors and broker-owner of Real Estate II in Coral Springs, Florida, called on the Federal Housing Administration to reduce the annual insurance premium it charges borrowers who put down less than 20 percent, saying the change will "expand options" for first-time buyers.

But Tobias Peter, a research analyst at the American Enterprise Institute's International Center of Housing Risk, and others at the conservative think tank say cutting the premium would place the mortgage insurance fund at risk of going below its congressional mandate.

Besides, Peter has a better idea, especially since today's market is hamstrung more by a lack of houses for sale than it is of people to buy them.

If NAR would ask its members to slash their slice of the deal by, say, 2 percent, might potential sellers jump at the chance to save $4,000 in commissions on a $200,000 house, or $6,000 on a $300,000 house?

Peter's hypothesis: "Just like any sale brings in new customers, the NAR's sale on commissions would single-handedly boost entry-level supply without driving up prices, as the NAR's calls for credit loosening have done. What is needed is more supply, not more demand."

Someone visiting one of Cindy Westfall's open houses a few years back swiped the seller's piggy bank. It was sitting on the dresser in the bedroom one minute, and then it was gone.

The Portland, Oregon, agent posted on the real estate website ActiveRain that, in eight years of holding open houses, "it was the first time I got a call from the seller saying something was missing."

Yes, the "five-finger discount" is alive and well in Realty Land. Face it: People like to touch and examine things at open houses. They like to open closets and drawers. Most of the time, it's innocent enough. But every once in a while, something goes missing.

Sometimes it's just one person who can't resist pocketing something and walking out. But sometimes, the thieves work in pairs: One keeps the agent occupied while the other roams from room to room, snatching whatever valuables he or she can find.

A few years ago, someone actually made off with a real estate agent's shoes. He had opted to remove them for the open house, rather than wear the floor-protecting blue booties that were available to prospective buyers. Michelle Carr-Crowe of Keller Williams in Cupertino, California, relates the story on ActiveRain: "It was not likely a mistake, as (the agent's) shoes were nearly new, inside and dry, whereas the 'trade-in' pair were old, well-worn and outside."

So, what are sellers -- and agents -- to do to protect themselves?

For starters, don't leave stuff lying around. That includes cash, checkbooks, credit cards, laptops or drugs, prescription or otherwise. It also means jewelry, watches and anything else thieves can shove in their pockets before making a clean getaway.

Also, take down any framed military discharge certificates. They sometimes include not only your name, but also your Social Security number. And log off the computer in your home office so people can't nose around and snatch your personal info.

Six years ago, a man in Silver Spring, Maryland, was arrested for stealing women's underwear from open houses. He was finally nabbed by an agent, who caught him rummaging through the owner's dresser. Turns out, the guy had dozens of women's undergarments from previous thefts.

Of course, while people tour your home, you can't carry the contents of your dresser with you. But where possible, you should keep valuables on your person, lock them up or remove them from your house altogether -- if not until the house is sold, then at least during an open house or showing.

Emmary Simpson of Long Realty in Tucson said she had an iPod lifted from a filing cabinet when she listed her house. After that, she removed everything of value, including expensive silver, and kept it at her parents' house. She also purchased a locking filing cabinet for items she needed to keep handy.

There are other precautions you can take, too. For example, make sure your bills and personal papers are out of sight. Don't just shove them in a drawer; organize them, box them up and put them away.

Guns and ammunition also need to be locked up and put away, if not removed from the house entirely. They tend to make would-be buyers nervous -- "If you need a weapon, is the neighborhood dangerous?" -- so remove them to another safe, locked location during the open house.

For you and your agent's personal protection, remove knife blocks from the kitchen counter. Every couple of years, an agent is attacked during an open house; don't provide would-be attackers with easily accessible weapons.

Also, make sure your open house is held by two agents. That way, one can welcome visitors and the other can walk with them as they tour.

That step would probably have stopped the couple who stole some $35,000 in jewelry from open houses in Montgomery County, Pennsylvania, a few years ago. The husband went to "look around" while the wife and kids occupied the agent. Or the two women in the New York area who made off with $73,000 in loot using the same tactic.

Another idea: Use "nanny cams" or other surveillance devices to keep watch on people as they move through your house. Or maybe just announce to visitors that cameras and microphones are hidden in every room.

Make sure your agent asks visitors for their driver's licenses and license plate numbers, and have the agent snap a picture of them and their IDs. Somewhat off-putting, perhaps, but the agent can say something like, "In this day and age, you can't be too careful."

Honest folks will understand, and the bad guys will move on to the next mark.

When people move to a new city, far away from where they once lived, the popular wisdom is to rent for a year before buying a home. That way, you have plenty of time to scope out numerous neighborhoods to determine exactly where you'd like to reside.

Seniors, though, have a different perspective. When they're checking out places to retire -- or join the 55-and-over "active adult" set -- their question is often, "How do I know I'm going to like the community I'm considering?"

That's the dilemma Mike and Robyn Bonitz faced when looking for a place to retire. After narrowing their choices to four retirement communities -- one in Summerville, South Carolina; one in Ocala, Florida; and two in Arizona -- the Connecticut couple gave all four a try, for a few days each. Now they're trying to decide between the two Arizona locations.

Staying at the properties for a few days "was extremely helpful," Mike says. "I would highly recommend it. You need a deep dive to see if these places live up to their reputations."

As it turns out, many major retirement properties offer so-called "discovery packages" similar to the ones the Bonitzes took advantage of. These "try before you buy" programs are an excellent way to experience the lifestyle as a resident.

I recently visited Sun City Festival in Buckeye, Arizona, which is one of the communities the Bonitzes are considering. I stayed with friends for six days, just across the street from the clubhouse and pool complex. I made great use of the workout room -- it was nice to lift weights with people my own age, as opposed to a bunch of young, muscular studs who make us old guys feel puny -- and the hot tub.

But had I known the Del Webb property offered a discovery package, I might have made use of that instead of inconveniencing my friends.

To attract buyers to Sun City Festival, the company offers furnished homes for two to four days, for up to four guests. They're not free, but the cost, depending on the time of year, ranges from just $49 a day for one or two people (in the summer) to $134 (in the high season, from February to April).

For that fee, you can live like an owner for a short while. The deal includes a golf cart, Wi-Fi, free use of the rec center, and golf at the residents' rate. The houses are outfitted with linens, towels, basic cookware and practically everything else you might need. Just turn the key and enjoy.

Sun City Festival opened in 2006, and some 3,000 people now live at the property. Residents enjoy amenities such as a golf course, tennis courts, cyber cafe, crafts center, classes sponsored by Arizona State University, numerous clubs and a playground for the grandkids.

Del Webb promises no high-pressure sales pitch with its discovery packages, but part of the deal is that you do have to meet with a sales consultant. Still, it beats staying in a hotel, and there's hardly a better way to relax and experience the property.

Sun City Festival is hardly the only place to offer a deal like this. Go to privatecommunites.com and click on the Discovery Packages tab to find dozens of others. Florida alone lists more than 30 places with "get acquainted" programs.

Here's the lowdown on a few other properties:

-- You can stay for four days and three nights at Retama Village, which is part of the Bentsen Palm gated community in Mission, Texas, in the Rio Grande Valley. No charge for folks 55 or older. The property has four unique neighborhoods designed for people of all ages. For sale are homes from $129,000 to $140,000, and lots from $20,000 to $90,000.

-- Shea Homes offers try-before-you-buy packages at all three of its Trilogy projects in California. For $299 at Trilogy at the Polo Club near Palm Springs, the "Taste the Good Life" program includes a three-day, two-night stay in a standard two-room hotel, plus a pair of spa tickets, a $100 dinner voucher -- and, of course, a tour with a sales rep. This active lifestyle resort will have 750 residences adjacent to two polo clubs. Prices range from the mid-$200,000s to more than $800,000.

-- At Soleil Laurel Canyon in the Georgia foothills in Canton, you can stay for three days, two nights in a fully furnished home with at least two bedrooms and two baths. For $79, you'll also get to enjoy a round of golf or tennis lessons for two, breakfast or lunch for two, and the obligatory private tour of the eight model homes, clubhouse and tennis center. The gated community has bocce ball, an arts and crafts center, greenhouse, outdoor amphitheater, walking trails and a horticulture center. Two- and three-bedroom ranch-style homes are priced from the low $200,000s into the $400,000s.