Sporting a tax return that includes a charitable donation of an Oldenburg rather than an old sofa? Or flush with an income in the seven-, eight-, or nine-figure range?

As affluent taxpayers map out their tax strategies, experts say they should pay close attention to following certain red-flag transactionss as they can act as audit magnets for the Internal Revenue Service.

Earned It? Then Report It.

"You always want to be careful and report all of your income," says Alan Olsen, a certified public accountant and managing partner with Greenstein, Rogoff, Olsen & Co., which specializes in providing financial advice to high-net-worth clients.

Sure an audit can result in painfully large penalties over rejected deductions. But fail to report income from the sale of a business, stocks sold, or a hedge fund that blossomed, and the check you may write in that case could be to a lawyer trying to keep you out of jail.

Weekend Vitner? Probably Not a Business.

Many founders believe that once they sell that start-up they nursed through 19-hour days, it's time to indulge other interests. But make sure, says Olsen, that you don't write off expenses from a lavender farm in Provence or vineyard in Napa as business deductions if they're really just hobbies and not producing an income.

"If you buy a winery, make sure you're out there cutting vines, and stay actively involved," Olsen says. "Don't go up there just once a year for a weekend, and expect the I.R.S. to allow your business loss."

Renting Out a Country Home?
Don't Camp Out for Summer.

Again, if you're looking for a vacation home, great. But if you're spending a month in your Tahoe condo for some late season skiing, and renting the space the rest of the year, it's no longer a rental property according to the I.R.S.

"Real estate is always a good investment to shelter some of your income," says Olsen. "But if you're buying something as an investment property, you can only stay less than 14 days a year. Otherwise, it's a second residence."

No Halvsies on the Rauschenberg.

Gone are the days when a modern art collector could grant a percentage of a painting to a museum—with a nice tax deduction—but actually get to keep it on the wall of the Manhattan penthouse until the donor's demise.

"There are significant restrictions on these fractional interests," says Elda Di Re, partner with the personal financial services arm of Ernst & Young, who says these kind of arrangements can send out big alarms to the I.R.S. "This has tightened up to the detriment of the museums," she says. And to the detriment of some sizeable write-offs.

Charity Needs the Right Receipts
—and the Right Appraisals.

Before donating the Prius to charity, make sure to secure proper, or so-called qualified appraisals, which does not mean fishing out the original bill of sale.

"There are very distinct requirements for qualified appraisals," says Ernst & Young's Di Re, who notes that often the actual signature of the appraiser must appear on the tax return. Plus, the appraisal must be from a place not related to where you originally bought the item—in other words, not the dealer.

Finally? The actual deduction may be limited to what the charity actually gets from selling the Prius, regardless of what you—and the appraiser—say it's worth.

Family-Run Business?
Careful About Management Fees.

The I.R.S. keeps a watchful eye for blurring between active and passive activities. Setting up a family company to run real estate holdings is fine, as is hiring the eldest son as the firm's vice president, and deducting his salary as business expense.

But hire a management firm to really do that work, and suddenly the son's salary may start to look like a dividend payment - and a passive activity. "That's not deductible," says Steve Parrish, a national advanced solutions consultant with the Principal Financial Group. "And to the I.R.S. that's taxable."

Don't Check K-1 Forms?
The I.R.S. Certainly Will.

Hedge funds and private equity firms report their partners' income on K-1's, which even tax experts consider to be rather confusing. But the I.R.S. is now focused on this income, concerned that much of it may have been underreported in the past.

It's also renewing efforts to match these earnings to what's reported on the taxpayer's return. Receiving a K-1? "This is where you want a specialist," says Di Re. Clearly.

Still, Flying High Brings Rewards.

One write-off that's not going to flag the taxman is a new provision made to Section 168 of the Internal Revenue Code. Never heard of it? That's okay, it's so new, it might not be on many C.P.A.'s radar yet either.

Essentially it reads like this: Pony up at least $200,000 on a factory-new airplane for business use this year, and you can write off half of the plane's value in its first year.

Crave that $40 million Gulfstream G550 but not sure you can justify the exorbitant price tag? Here's the ultimate excuse. Perfect for that angel investor jetting from coast to coast to check on his investments, or even professional athletes, like Tiger Woods, who prefer some alone time between tournaments.

After all, who says that golf isn't work?