Anything that runs on electric power or is a big ticket item requires a little research, both into the tool and the seller, before you buy it second hand. Hand tools, however, are generally great yard sale bargains. Hammers, saws, wrenches, and the like don't get very much use unless the owner prior owner was particularly handy. Most tool boxes only leave the closet or garage every few months, and even then only a couple tools get any use. Also consider how often you plan on taking the tools for a spin once you buy them. If you're just using a hammer to put up pictures and your screwdrivers are for pre-fab furniture assembly, there's no reason to give Home Depot any of your hard earned cash.