Most buyers who purchase existing houses use the services of a real estate professional to help navigate the intricacies of the transaction. But do you need an agent when you are purchasing a brand-new home?

When Ritu Desai bought her first new house in 1999, she flew solo. Now, as a real estate agent with Samson Properties in Chantilly, Virginia, she realizes she made a big mistake.

Desai says she "regret(s) to this day" not having an agent represent her interests when dealing with her builder. She uses this personal experience to warn her clients that they need representation when dealing with a builder.

Many builders tend to disagree. While some builders welcome agents who bring would-be buyers to their model homes or sales trailers, many would just as soon see the agents disappear once the buyer shows real interest in purchasing a house.

The attitude is: "Thanks for bringing us this buyer. We'll take it from here."

But Desai and many of her colleagues argue that new-home buyers need someone to represent their interests, just as folks who purchase existing homes do.

"Sure, lots of people go it alone," says R. Bruce Lynn, a broker-associate at Keller Williams Realty in Coppell, Texas. "But they often could get a better price, a better house and a lot less headaches" by using an agent --ideally, a specially trained buyer's agent.

Cara Ameer, an associate broker with Coldwell Banker Vanguard Realty in Ponte Vedra Beach, Florida, agrees: "To undertake what is your single largest purchase without any representation is simply being foolish."

First, let's talk price: As part of their marketing budgets, builders include commissions they'll have to pay agents who bring them buyers. That's anywhere from 2 percent to 4 percent, or $4,000-$8,000 on $200,000 house. And if there is no agent, they take that money directly to their bottom lines.

But since that money is already built into the builder's price, solo buyers should be able to persuade the builder to lop off at least some of it from the cost of the house. After all, some builders' profit margins are high enough as it is.

But if you have an agent, the builder pays the commission, not you. So it costs you nothing to use an agent, and the "savings" could be well worth the price.

Money isn't everything, though. So here are a few other reasons why an agent could prove invaluable:

While it is common knowledge that everything is negotiable when you are buying an existing house, most people don't realize that the same is true when the house in question is brand-spanking-new.

"Buyers are often so focused on price that they don't know they can bargain" with the builder, says agent Lynn.

Builders won't be nearly as flexible as individual sellers. But a seasoned agent who is familiar with the new home market -- or even familiar with your particular builder -- may be able to sway the builder to throw in a couple of extras, move a wall here or there without cost, or maybe even lower the price a bit.

Good agents will also advise their clients to obtain an independent home inspection, just like they would if the house was a resale. Most people get so caught up in the glitz of a new house that they don't think about an inspection. After all, they equate "new" with "perfect," but that's hardly the case.

"I've never seen an inspection on a new house that didn't have a laundry list of issues," says Lynn. And these are often issues that you may not notice when you do your own final walk-through, but that need to be corrected before you move in.

Rae Catanese of RE/MAX Bay to Bay in Tampa, Florida, had a client whose builder vowed an inspection was unnecessary. But her buyers hired an inspector anyway, who turned up some sloppy drywall work and unfinished trim, among other things.

"Ultimately, the builder fixed everything," Catanese says.

And then there's the builder's sales contract, which is usually incredibly one-sided. With a veteran agent speaking for you, the builder might be willing to eliminate a few of the more onerous clauses.

"An experienced agent will make sure that everything you want, or any matters related to the transaction, are stated in the purchase contract," says Dao Alderman, an associate broker with Keller Williams in New Tampa, Florida. "Even if it seems unimportant, it could cost you in the end if it's not part of the contract."

Warranties are another issue. Builders almost always provide a one-year warranty against workmanship and defects, and some offer 10-year protection against major structural flaws. But do you know what's actually covered and what's not?

"A good real estate agent who handles new construction will ask the necessary questions," says Florida agent Ameer. For instance: Which aspects of the home are covered under the builder's warranty, and for how long? Who administers the warranty?

The bottom line is this: The builder and their salespeople represent themselves and their interests, which are not always aligned with yours. Consequently, it is always a good idea to have another set of eyes and ears on your side of the table.

Let this be a lesson, from one of Desai's clients . Midway through the construction process, it was discovered that a very important option was not in the house, even though it was in the contract.

When the mistake was pointed out to the builder's agent, the buyers were told they would have to pay extra for it. But with Desai arguing on their behalf, the builder backed down and agreed to adhere to the contract.

"I am not dropping a child off at day care," says Desai. "I stand by my clients."

While many homebuyers, especially younger ones, now prefer to do their shopping online, most lenders are still warming to the idea that borrowers also would rather use their laptops, tablets and even smartphones to take out a mortgage.

Just as technology has not replaced a good real estate agent, it's doubtful it will replace a knowledgeable loan officer who can explain something when necessary. But to smooth the transaction and make it more comfortable for today's borrowers, the lending community is working hard to meet clients on their terms.

In a few weeks, for example, mortgage giant Fannie Mae will roll out an electronic mortgage app that will be able to verify a borrower's income using data from third-party sources.

With the new app, there will be no need for the borrower to deliver pay stubs to the lender. With a click, the lender can access the necessary information faster and more securely, a common concern for both borrowers and lenders.

Fannie Mae also is working on similar validation services for other required borrower income documents, such as bank statements and tax returns.

According to Jane Severn, Fannie Mae's director of product development, the idea of applying for funding online is gaining traction among borrowers who tend to be younger or at the high end of the price spectrum, and "are most active at 10 p.m. when they feel they don't need a loan officer and they're ready to go."

The art of "flipping" -- buying a house, fixing it up and reselling it within months or even days -- is still alive and well in America. According to RealtyTrac, 5.5 percent of all home sales last year were flips in which the property sold in an arm's-length transaction for the second time within 12 months.

But flippers beware: Uncle Sam may have his eye on you. The tax treatment of quick turnarounds hinges on whether the Internal Revenue Service sees you as a real estate dealer or investor.

If you are a dealer, net income is subject to the regular income tax plus the 15.3 percent self-employment tax, which is based on the first $118,500 of adjusted net self-employment income. The holding period of the house is irrelevant.

If you are an investor, on the other hand, net income from properties held a year or less is considered to be short-term capital gains, which are generally taxed at the taxpayer's ordinary income rate or bracket, from 10 to 39.6 percent.

"Investor" is probably the preferred title of most flippers, but the IRS has a list of factors it considers when making the determination, and no single one is more important than the other. Each finding is based on the circumstances surrounding each individual sale.

One factor is the number of flips per year. One or two does not normally trigger dealer status, but as the number rises, so do the chances that the tax collector will view the flipper as a dealer.

Other questions the IRS wants answered: How quickly was the property resold? Is the taxpayer a real estate professional? Is the taxpayer flipping houses full time? What percentage of the taxpayer's income comes from flipping?

One tax benefit available only to dealers is that they can deduct their total losses in the year they were incurred. Conversely, both an investor's long-term and short-term losses may be limited to $3,000 a year, depending on the investor's other capital gains or losses. But the remaining losses can be rolled over to the following year or years.

Would-be homebuyers would be wise to apply for their financing in locations where it is usually sunny, according to a working paper from the Cleveland Federal Reserve Bank.

Using data from the National Oceanic and Atmospheric Administration, researchers found that loan approvals are higher when the sun is out. Approvals drop by 1.4 percent on cloudy days, but rise 0.8 percent when the sun is shining.

These are not insignificant shifts. "A rough estimate of the extra credit approved on one perfectly sunny day relative to one fully overcast day is about $150 million nationwide, or $91,000 per county-day," the paper says.

The bad news: Loans cleared on sunny days experience significantly higher defaults, the researchers found.

Most homebuyers base what they are going to be spending every month for their new digs on how much they are borrowing and the interest rate they're paying. But if that's all they consider, they are missing a big component of their monthly housing costs -- their utilities.

What's more, the cost of gas, oil and/or electricity to heat and cool the house is only one part of potential utility bills. Unless you will be using a well for your water and a septic tank for your sewer, you'll have to pay for those conveniences every month, too. And then there's trash removal and possibly even homeowner association fees.

The total cost for these necessities could add as much as 25 percent of your mortgage payment to your total monthly housing costs. Depending on the size of the place and how often you run your dishwasher and dryer, the outlay for utilities could run as much as $500 a month. Maybe even more.

Fortunately, if you are purchasing an existing house, it won't be terribly difficult to estimate your utility bills. At least, not if you have a cooperative seller.

Ask the seller for a list of what he or she paid for the various segments of utilities for the last 12 months. It may be a chore to compile, but bills just for the last month or two won't be terribly meaningful.

Of course, your monthly bills might be different from the seller's. You might be setting your thermostat higher or lower, depending on your comfort level, for example.

You might use more or less water, depending on the number of people in your household and how hot they like their showers and baths. And your kids might be running in and out all day long, which will run up your heating and cooling bills. But at least you'll have a decent approximation of what your costs will be.

Another way to estimate your costs is to use one or two or maybe even three of the various online utility estimators. They aren't pinpoint accurate, and as noted above, how you use the place will have a great deal to do with your monthly outlays. But again, they will give you an idea of what you'll have to spend in addition to your mortgage payment.

Myutilityscore.com is one of the newer sites. Simply plug in your new address, and it will divine your monthly, yearly and peak costs for electricity, gas and water. The site also will estimate your total annual bill and give you an overall score of one to 100, with 100 being the lowest costs.

It also will allow you to refine your estimates by adjusting for the number of people who occupy the house, your intended thermostat settings for winter and summer, and whether or not the place will be occupied during the day.

CPSEnergy.com has separate calculators for appliances, ghost-energy (plugged-in appliances use energy, even when they are turned off), heat pumps, televisions and lighting, plus an overall home energy calculator. These appear to be somewhat more cumbersome to use, but they still do the trick. (San Antonio-based CPSEnergy is the country's largest municipally owned energy utility.)

General Electric has a detailed electric cost calculator that also includes lighting and personal appliances, and a Home Energy Saver (energy.gov/energysaver/energy-saver) estimator from Uncle Sam that allows you to estimate your annual costs plus the cost to operate specific products.

In addition, look for the EnergyGuide label, the yellow tag you'll find attached to most appliances. It tells how much energy an appliance uses. Add the figures up and you'll have something approximating what you will be spending every month.

As you can see, trying to determine what your costs will be for a brand-new house is somewhat more problematic, if only because the place has never been occupied. But savvy builders will have asked the local utilities to provide estimates of what it will cost to run the house.

If your builder hasn't already done so, you can call each provider and ask for an estimate. Not all gas and electric companies do this for individuals, but it is worth a try, nonetheless. (With some, it's a mixed bag.)

Assuming all the major electrical equipment is installed, Potomac Electric Power Co. (PEPCO) in the Washington, D.C. area will "come out and give a customer an energy bill estimate," a spokesman said.

For people buying existing homes in suburban Maryland, PEPCO will send them the previous 12 months' worth of utility bills on the property so they can gauge their energy costs. And if you are an existing customer moving to a new total-electric house, you can enter your account number to use PEPCO's online energy cost calculator.

Finally, if you are willing to spend a little cash -- and your builder is willing to do so -- hire an energy-auditing firm to estimate how much your utility bills should run. Savvy builders will have done so for each of their models. But if yours hasn't, pay a certified auditor using a generally accepted index such as HERS, which stands for Home Energy Rating System, to give you an idea of your monthly outlay.