AS YOU APPROACH, THEN

enter retirement, salesmen for offbeat investments from annuities to Zambian coffee plantations will try to pitch you their products. They know you have been accumulating savings and are contemplating major life changes. They also hope that after decades of working hard and playing by the rules, you're harboring a Kramdenesque longing to be part of a quick big score. My Uncle Walter started a successful insurance agency and put three kids through college. He also once bought a special knife because a neighbor told him it would cut through a penny.

He's the ideal target for a time-share sales presentation.

Time-share property is a place that you own (or have the right to use) in conjunction with other people and that each owner occupies for a particular period every year. The concept dates back to a French ski resort developer named Paul Doumier, who began offering travelers the chance to buy rather than rent hotel rooms in the mid-1960s, and time-shares first sold in the U.S. in Hawaii in 1969. They've really taken off in recent years, as aging boomers and empty nesters have sought to acquire second homes and vacation spots even if they have to do it on a part-time basis and to shift their assets from stocks to real estate. More than four million households owned stakes in time-shares in 2005, according to the American Resort Development Association. Despite choppiness in the overall real estate market, that number was up 5% from 2004. The average age of recent buyers? Fifty-two.

Part of the appeal of time-shares is the burgeoning market for exchanging vacations. If you buy one week of time-share at a Colorado resort, you can travel there annually, or trade your days for a week in the California desert or the Canary Islands or even New York City. Further, time-shares are usually condominiums, which can make them much cheaper to stay in for multigenerational families than blocks of hotel rooms. And you can often leave your time-share to your heirs.

But for a product that's been around for 40 years and is perfectly legal, the time-share business is remarkably rife with slimy sales tactics. You don't see too many TV commercials or magazine ads for time-shares. Instead, developers are still in the habit, acquired in the early days of the business, of making unsolicited offers of "free" gifts and "no obligation" vacations to travelers willing to attend sales presentations. You've probably received these offers in your mailbox, and you also may have gotten them from "off-property consultants" who set up booths in hotels and troll high-traffic vacation areas like Cancun beaches and the Vegas strip. In the bad old days, travelers who said yes to these solicitations found the gifts were frequently awful (a new toaster!), the presentations were long and stressful, and all too often, the developers were financially shady.

In recent years sales practices have improved, thanks to state laws and industry self-regulation. But outright fraud still exists and most of it is aimed directly at retirees. The state of Missouri, for example, just shut down a group of time-share operators for taking a total of $1.8 million from some 40 residents ages 64 to 86 without telling them they'd bear sole responsibility for managing their Cancun condos. In addition, many time-share buyers are surprised by a host of issues: unexpected fees, problems trading weeks, disappointment in the quality or location of the property, or that the return fails to appear. All of which goes back to the transparency of the original transaction. This is a business where Lisa Ann Schreier, author of Timeshare Vacations for Dummies, still felt in 2005 that she needed to advise: "Don't buy any time-share if you're offered alcohol prior to or while signing anything."

Having said all that, time-shares can be a perfectly reasonable purchase just stay informed. The basic idea is to buy a place that you'll want to visit every year or that is in high demand among other travelers. Time-shares, like cars, suffer most of their depreciation early on. So you must expect to get value from your own enjoyment of a time-share or in trade for other vacation spots, not from reselling it for cash.

To judge the merits of time-shares, get familiar with the business. You should know that while many are deeded properties, others (especially outside the U.S.) are leases or right-to-use agreements, which don't give you permanent real estate ownership. Also, vacation weeks come in three flavors: fixed (the same slot every year), floating (you can reserve different times in different years) and point-based. Under point-based systems, which are used by several of the giant hotel companies that operate time-shares, such as Disney, Marriott and Starwood, time-shares have specific values depending on the location of your resort and the time of year you stay. You can use the points to stay at any locale and sometimes for airline tickets or car rentals, too. Also key: The trade value of your property will be determined by whatever time-share exchange company is affiliated with your resort. That firm will handle transactions between your time-share and others around the globe, usually for a fee of about $160 per trade. The two largest are Resort Condominium International, owned by Wyndham Worldwide, and Interval International, owned by InterActiveCorp. For more details on ownership, use and trading, buy Schreier's book and join the Timeshare Users Group, or TUG (www.tug2.net.

Beyond learning about the industry, here are three rules to follow:

First, skip the shtick. You don't need to go to a sales presentation to buy a time-share. And you shouldn't want to, for reasons that go beyond not wanting to revisit Glengarry Glen Ross. You can save 10% to 50% by purchasing a time-share that's just a few years old. This also allows you to talk with actual owners of time-shares, not just sales staff. So check TUG, your local real estate listings and Internet auction sites for time-share resales.

Second, pay cash or don't pay at all. Because time-share developers essentially will offer financing to anyone who walks through their doors, they typically charge whopping interest of about 16%. Paying that is like putting 20 years of vacations on a credit card all at once, which just doesn't make sense. The average cost of one week of time-share is about $16,000, according to ARDA. If you don't have something like that amount of cash to play with, take annual vacations, and stay away from time-shares until you do.

Third, if the time-share you're interested in uses a point system, make sure it's inflation-proof. If it takes 10,000 points to stay in New Mexico for a week this year, ensure that similar stays will cost 10,000 points again next year or that your points will increase by however much prices are going up. Some time-shares lure buyers into a point system, then hike costs, forcing you to buy more points just to stay even with your original purchase. If you can't get a guarantee that your points are protected from such shenanigans, walk away.

Finally, keep in mind that if you find a sensible time-share deal, the decision to buy will be as much psychological as financial. If you like traveling to the same spot for a week or two every year, or if the idea of playing a vacations market appeals to you, you're a time-share person. If you enjoy booking trips without having to follow any set rules, or if your ideal getaway is a house in the woods that nobody else can touch, you're not.