Helmets. Helmets are designed to protect you from one accident, and one accident only. Sometimes damage isn’t visible, so buy a new helmet to make sure you’re getting full protection.
Tires. If they’ve been in an accident, tires are likely to be unstable and unreliable. Make sure you can get an accurate history.
Child car seats. Like helmets, car seats are really only meant to protect in one accident. But damaged car seats are common; a survey found that one in ten have been in an accident. Plus, car seat technology improves each year.
Wet suits and swimsuits. Personal products that hug your body are technically safe if you wash them in hot water...but still be cautious. Constant changes in water pressure also wear out swimwear faster than regular clothing, so it's likely a used wetsuit or swimsuit will tear.
Cribs. Scores of crib recalls, as well as changing safety standards, make it hard to verify the safety of a used crib.
Laptops. Laptops are more likely to be dropped, knocked around and spilled on, simply because they’re out in the world, while a desktop computer sits (mostly) safe at home.
Running shoes. Used running shoes are often devoid of the cushioning that runners need; stick with new shoes for the cushioning and fit that will protect knees, feet, and legs.
Sheets and Pillowcases. Sure, you can wash them in hot water, but that might not protect against bed bugs.
Baby bottles. While sanitation and cracks can be an issue, the real culprit is the chemical BPA that's present in most older bottles—and as of June 2012, the FDA no longer accepts that as safe. Go with new bottles to make sure you're getting the safest, most up-to-date bottles.
DVDs, CDs, and VHS tapes. Scratches have ruined many a DVD or CD—and VHS tapes can lessen in quality the more times they're played, and disintegrate over the years.
Worn plates, pots, and other cookware. Rust, flaky non-stick coatings, and chemicals that leach out are just a few of the safety problems you can run into with older cookware.
Clothes that require a tailored fit. It might look like it fits—until you put it on. Unless you can try something on, it's often not worth the money you'll spend on alterations.
Upholstered furniture. Just like mattresses and sheets, any upholstered furniture can be home to bed bugs, fleas, and spiders, as well as unknown odors and stains. Unless you're going to reupholster the piece, steer clear.
Video Games. You might want to quickly google the video game—manufacturers are now including codes for one-user only play, either for the whole game or special bonus sections.
Stuffed animals. Stuffed animals can be hard to send through the extra-hot cycle on a washing machine, and like mattresses and upholstered furniture, they can be full of creepy crawlies and other unsavory finds.
Blenders and other kitchen electronics. Blades and mechanisms can become dull and wear down over time, even if the machine looks fine on the surface.
Hats. How's this for gross: Hats may contain remnants of hair products, sweat, or skin infections.
Fragrance or makeup (new or old!). The quality of both can lessen over the years (and yes, they do expire!). Even if an item is brand new in the box, skip it unless you can tell that it was recently manufactured.