Things you should never buy used

Sometimes the financial or safety risk outweighs the savings. Do you really want to sleep on someone else's mattress?

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.

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 currently in use in that country had been involved in an accident. (The bank is calling for a ban on the sale of secondhand seats.)
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.

Plasma 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 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 plasma 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.

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.

Camcorders Someday they'll build a camcorder 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. Camcorder motors can also wear out and may cost you a couple hundred dollars to replace.
If you want to save money on a camcorder, consider buying last year's model.

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. 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.

Mattresses Think of all the stuff you do on your mattress. Now think of sleeping in someone else's stuff. Ewwwww. There's also the fact that mattresses aren't meant to last forever. Even the good ones typically have a life span of just eight to 10 years, and it's hard to know for sure how old a used mattress may already be.

Helmets Like a car seat, a helmet is meant to protect against one accident and no more. A crash typically crushes the foam inside the helmet casing, according to the Bicycle Helmet Safety Institute, so the damage may not be visible. Since you usually can't tell if a helmet's ticket has already been punched, you're smarter to buy new. Kid's sports and bike helmets retail for about $20; you'll pay $30 to $40 for the adult size. Motorcycle helmets usually start around $100 and climb steeply from there; you can contain the cost by resisting the fancy paint jobs.