WHEN YOU'RE SHELLING

out $3,000 for a 50-inch flat-screen TV, it's nerve-wracking to hear a salesperson explain what

go wrong if you pass up the offer to buy an extended warranty. What if it falls from the wall mount? What if the pixels get damaged? For the most part, those fears are unwarranted.

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"The numbers game is stacked solidly in the retailers' favor," says David Carnoy, executive editor of electronics review site CNET. Shoppers pay roughly one-third the item's price for a two-year warranty extension. Of that, retailers pocket about 80% as profit merely because consumers are often unlikely to use their warranty or need a costly repair during the coverage period. That's one reason why store employees are so quick to push extended warranties and service plans for everything from flat-screen TVs to microwaves.

However, there are a few exceptions to the warranties-aren't-worth-it rule. Just don't expect blanket recommendations (i.e., always buy for iPods, never for refrigerators). The choice to buy or not to buy is entirely situational. If you and your purchase fit several of these conditions, an extended warranty or service plan may be worth a hard second look:

If you are:

Not tech savvy

. Because extended warranties often include tech support, they can be cost-effective for consumers who need a lot of handholding, says Carnoy. Apple's MacBook laptops, for example, come with just 90 days of tech support. Thereafter, each call costs $49. But pay $249 for a three-year AppleCare Protection Plan, and you've recouped the cost after just five calls, necessary repairs notwithstanding.

Clumsy. One slip of the hand or careless swing of the knapsack can wreak havoc on fragile gadgets. That damage isn't usually covered by a manufacturer's warranty, warns Jerry Grossman, editorial director for tech education site DemystifyingDigital.com. Some extended warranties, on the other hand, tend to forgive you for such accidents, as well as even loss or theft. You'd pay $5.99 per month for handset insurance on your T-Mobile Sidekick LX, plus a $110 deductible to replace the $400 phone. So if you damage it to the point that it needs to be replaced within the first 48 months of ownership, you could come out ahead.

Heavily using the item. Someone who cooks as if every day is Thanksgiving with all four burners and the oven on simultaneously for hours is going to inflict more wear and tear on his stove than a consumer who prefers takeout. So if you know that you're going to be using an appliance or gadget to its full capacity and on an almost daily basis, odds are that it will likely require repairs during the extended warranty period, says Dale Haines, a senior director at J.D. Power and Associates.

Your gadget is:

Cutting-edge

. "If it's something that's not tried and true, an extended warranty may be worth it," says Carolyn Forte, homecare director for the Good Housekeeping Institute. Without a long-term record of reliability, it's tough to say what problems will pop up with your cool, new gadget and when those issues might occur. Take Microsoft's Xbox 360, which sold out nationwide within two hours of its November 2005 release. Service problems have since plagued the console, including a hardware failure gamers have nicknamed the "red ring of death," overheating, and an August 2006 software update that rendered some consoles useless. The initial warranty period: just 90 days, with repairs thereafter costing $140 each roughly one-third the initial $400 console price. A two-year extended warranty from Microsoft would have cost $60.

The problems were so widespread that in December 2006, Microsoft extended the manufacturer's warranty to one year; and then, last July, extended it again to three years, pledging to reimburse consumers for their repair bills. But that kind of bailout is rare. For early adopters, it's better to be safe than sorry.

Refurbished. If you're buying a refurbished item, floor model or open-box unit, the terms of the initial warranty you get with the product can be far from adequate, says Tom Spring, a senior writer for PC World magazine. Olympus, for example, offers a one-year warranty on most new cameras, binoculars and other products. However, refurbished models are covered for just 90 days.

Pricey. The more expensive the item, the more thought you ought to put into an extended warranty, says Grossman. "Weigh it in terms of replacement costs for the item," he says. "How much is it worth spending to protect that asset?" For help, look to Consumer Reports' online "Repair or Replace" guidelines, which list average costs for both options. Say you're about to pay $2,500 for a Dell XPS M2010 laptop computer. If shelling out an equal amount next year to replace it, or the average $400 it costs for each repair, amounts to a crushing financial blow, spending an extra $200 now for a one-year warranty extension may be the lesser of two evils.

Prone to problems. Read expert and consumer reviews, and you'll discover some gadgets are more likely to require a pricey fix within the extended warranty period than others. Rear-projection TVs are a prime example. In fact, rear-projection TVs are three times more likely to require repairs than other kinds of sets, according to Consumer Reports. The culprit: The $300 bulb that powers the set has an estimated life of just 5,000 hours. Given that the average American watches more than four hours of TV a day, it's likely that the bulb could blow within a three-year extended warranty period.