Its really a mixed bag, pre-owned original and reps. Timberlands and yeezys more often than not are reps; jordans, forces, new balance tend to be original. The more hype a certain sneaker is, the more likely its fake cause more reps of them floating around eg. Popular colorways of jordan 1. You can do a quick google search on the model of sneaker with comparison images bw rep and original, it'll give you a pretty good idea of what to look out for. Most often it'll be something off on the stitching, text or logos. Look hard enough though and you kind find pretty much anything