For many types of durable consumer goods, "shop secondhand" is a valuable money-saving tip. Books, cars, dishware, décor, and most clothes can often be bought for pennies on the dollar compared with their normal retail prices. But sometimes buying used can be a waste of money or even be dangerous. The following items should always be bought brand-new, either for safety or hygienic reasons.
Modern safety helmets are essentially "single-use" items, designed to absorb the impact of one crash. After that one crash, the helmet is useless. But most, if not all, of the damage is to the helmet's internal structure, invisible to the naked eye. It's impossible to know the history of a used helmet, so buy a new one from a reputable retailer.
As with safety helmets, child car seats can be damaged in ways the eye can't see. Older car seats also might not conform to modern safety standards.
No two people's feet are exactly alike. Shoes, sandals, boots, and other footwear conform to the shape of their original owner's feet, which is sure to be different from yours.
These items were worn in too-close proximity to their previous owners' feet and nether regions. New garments can already be bought so inexpensively that the savings would be negligible.
Used bathing suits have the same hygiene problems as used underwear. Even if that weren't an issue, swimsuits tend to wear out quickly; an old suit might fit when it's dry but sag or stretch out as soon as it gets wet.
How clean was the previous owner's hair? There's no way of knowing. Machine-washable knit hats might be safe to buy used, but fedoras, cloches, and other wool or felt "shaped" hats generally are not. Such hats must be cleaned professionally, and the cost would likely negate any savings compared with simply buying the hat new.
Antique cribs, changing tables, and other baby furniture are often unsafe by modern standards. Even with more contemporary baby furniture, far too many pieces have been subject to safety recalls. The Consumer Product Safety Commission maintains a searchable recall page.
Mattresses are essentially impossible to clean, and a used one is certain to hold some of its previous owners' dead skin, dust mites, and dried bodily fluids. Even worse, mattresses and pillows might contain bedbugs.
These furniture items share many of the same problems as mattresses -- even if they look clean on the outside, the upholstery can be dirty or even bug-infested on the inside.