To be honest, I've always been skeptical about used boots. You have no idea what that guy did with those boots or what happened to them. Just speaking from my old pair, they were wridden to shit. But they still look brand new.
I look at buying a used pair of boots like it would be to buy a used mattress from someone random. It may be cheaper and seems like a good idea, but once you get in the thing and realize its all lumpy and moldy or smells, you regret it. I'd just look into a new boot you can try on and know that it has no shady past. But thats just me.