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Saving money by surfing the Internet for bargains is delightful, but you can take it too far.

In my companion piece, "10 things you shouldn't buy new," I listed lingerie as one of the items for which you'd best pay retail. There are plenty of other examples where the cost savings don't justify the risks of buying used:

Laptops

You're taking a chance when you buy any used computer, but the math really doesn't work when you're talking about a unit that's as prone to abuse and problems as a laptop. They're more likely to be dropped, banged around and spilled on, simply because they're out in the world while a desktop computer sits (mostly) safe at home.

That's why laptops are one of the few products where springing for an extended warranty with free tech support makes sense, in addition to the standard warranty that typically comes when you buy new. Buy used, and you'll have neither option -- along with no idea what maltreatment your laptop has suffered or when the hard drive, optical drive or other important parts will die on you.

Exception: You're buying a refurbished unit that comes with a warranty. Mobile technology consultant Catherine Roseberry, who writes a column for About.com, said she's purchased two laptops from companies that refurbished leased corporate computers, and had no problems with either. Both came with 90-day warranties. If you want even more security, buy a laptop that's been refurbished and certified by the manufacturer.

Car seats

A car seat that's been in one accident may not protect your child in another. And damaged car seats aren't uncommon; a survey commissioned by Sainsbury's Bank in England discovered one in 10 car seats in use in that country had been involved in an accident.

Liz Weston

Liz Weston

Brand-new car seats can often be purchased for as little as $50, and safety technology tends to improve with each year, said Denise and Alan Fields, parents and authors of "Baby Bargains." That makes getting a new one pretty much a no-brainer.

Exception: You're getting the car seat from a friend or relative whom you'd trust with your child's life, because that's what you're doing. Still, check with the National Highway Traffic Safety Administration to make sure the model you're getting hasn't been recalled.

Regardless of whether you buy new or used, have an expert check your work to make sure the seat is installed correctly. The NHTSA has a list of free inspection sites at its website.

Plasma and high-definition TVs

Here's another of those rare cases where you want not only the warranty that comes with the television, but an extended warranty. You'll want the coverage because if your screen dies, it can cost hundreds or thousands to fix or replace -- sometimes almost as much as it would cost to buy a new TV.

While defect rates have declined from 7% in digital TV's early years to about 1% with some of the better models, problems with this technology are still common enough -- and repairs expensive enough -- that an extended warranty makes sense, said Phil Connor of PlasmaTVBuyingGuide.com.

Exception: If you're getting such a screaming deal that you don't really care if the TV blinks out shortly after you get it home.

DVD players

In the previous article, I recommended buying used DVDs, since their quality tends to remain high (unless they have scratches, which are usually pretty easy to spot).

The same is not true of DVD players, however. These have lasers that will eventually wear out and cost more to replace than the unit is worth.

Whenever repairs cost that much, buying new is often advisable. Add to that the fact that prices are constantly dropping while the technology is constantly improving, and buying new becomes a slam dunk.

Vacuum cleaners

Here's another item that's particularly prone to abuse and that may cost you more to fix than if you'd simply bought new. Consumer Reports says a good, basic upright can be purchased new for less than $100, and that the fancy features that push prices higher often aren't worth the extra cost. Just make sure to buy one that you're comfortable pushing and that has a decent filtration system to prevent dust from kicking back out into the air.

Exception: You're handy and don't mind teaching yourself vacuum repair.

Digital cameras and video cameras

Someday they'll build a camera out of rubber, so that it'll bounce when you drop it, which is almost inevitable. The damage from a fall may not be obvious when you buy used, but it may soon require a costly repair.

If you want to save money on a digital shooter, consider buying last year's model.

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Exception: You're buying a refurbished model that comes with a warranty. RefurbDepot.com, for example, posts many models that still carry a factory warranty.

Shoes

Poor-fitting shoes can cause everything from bunions to back problems, so don't buy footwear that's already been molded by someone else's tootsies. This is particularly important for kids whose feet are still growing. Shop sales, buy last year's models, but don't give in to the temptation to save a buck now that's going to cost you more in pain and hassles later.

Exception: You're buying old cowboy boots to turn into lamps.