I furnished my first apartment almost entirely from thrift stores and Craigslist. Some of those purchases — a solid wood dining table for forty dollars — are still in my house ten years later. Others — a used mattress I do not want to think about — were mistakes I would not repeat.

Buying used is one of the best money-saving moves you can make, but some categories are worth it and some absolutely are not. Here is my list after a decade of trial, error, and one particularly ill-advised used vacuum cleaner.

Always Buy Used: Solid Wood Furniture

New furniture is either expensive or particle board. Used solid wood furniture — dining tables, dressers, bookcases, desks — is cheaper and better built than anything you can buy new for the same price. Look for dovetail joints (not staples), real wood (not veneer over particle board), and sturdy legs. A forty-dollar dresser from a thrift store will outlast a two-hundred-dollar flat-pack from a big box store.

Always Buy Used: Cast Iron and Quality Cookware

Cast iron pans, Le Creuset, All-Clad, good kitchen knives — these things last decades or lifetimes. A used Le Creuset Dutch oven with a chipped exterior but perfect interior costs eighty dollars instead of four hundred. Estate sales are especially good for this. Old people had good cookware.

Always Buy Used: Kids’ Clothes and Baby Gear

Kids outgrow clothes in months. Used baby clothes are often worn two or three times before they are outgrown. Thrift stores, Facebook Marketplace, and parent swap groups are goldmines. Strollers, high chairs, and bouncers — same thing. Clean them thoroughly and save hundreds.

Never Buy Used: Mattresses and Upholstered Furniture

Bed bugs, dust mites, and mystery stains. Just do not. A mattress is something you spend a third of your life on; buy it new. Upholstered couches and chairs can harbor pests and odors that are impossible to fully remove. If you must buy a used couch, inspect every seam with a flashlight first.

Never Buy Used: Car Seats and Bike Helmets

Safety gear that has been in an accident may have invisible structural damage. Car seats also expire — the plastic degrades over time. A used car seat from a stranger has an unknown history. Buy these new. The money you save is not worth the risk.

Never Buy Used: Cheap Electronics

A used iPhone from a reputable refurbisher with a warranty? Fine. A used toaster from a garage sale? Not worth the fire risk. Anything with a heating element, cheap motor, or non-replaceable battery — buy it new. Cheap electronics are already barely reliable; used cheap electronics are a gamble with bad odds.