I'd be more worried about buying slick road tires used. My experience is that road tires break down over time or something such that they become more prone to flats even while the tread appears to be fine. Also, it's nearly impossible to judge how much wear a slick has experienced until it's almost completely worthless. Not so with off-road tires. It helps if you know what the tread looked like when it was new, but generally off-road tires wear in a fairly visible way.


I think CX tires are a particularly good choice for buying used because CX racers tend to really geek out over their tires and thus are much more likely than the average bike user to want to get rid of a perfectly good tire.