I once ordered a used book from the internet, supposedly in very good condition - when it arrived it was in a state that I can only describe as grubby, covered in what I assumed (and hoped) were tea/coffee stains, basically it looked like it had been dropped in a very large muddy puddle, and I wouldn't give a book in that condition to anyone. So I'd only buy a used book if it was in very good condition, I don't mind a few mild spinal creases and slightly foxed pages, and generally the used books I have ordered have been in v good condition - some look as if they'd hardly been read (a bit like my own books). But I'm careful now who I order from, I think I've learnt which sites to trust!