"The computer could be slow, infected with a virus, or have damaged hardware and you might not realize this until it's too late. Buying a used laptop or computer is a gamble when it comes to computer safety." ---you tell the owner you're a serious buyer ---if you can test it presently with whatever software you're going to use for an hour ---play music, run videos, ----test all ports, ----battery, ---you tell them to leave it running for a couple of hours ----if they're bothered dont even bother.... ---run it through like you would do for a car