I only purchase from this website when I come across something I really want to buy, e.g. book merchandise (I'm a bookworm). I've had about three experiences with different sellers. The first 2 sellers were polite and helpful, and my items arrived as promised. The last seller I dealt with, was quite abrupt (he replied curtly and I felt annoyed with him) and I felt quite uneasy about making a purchase from him so I backed out of the deal as politely as I could.
Given the fact that this is a marketplace, I would say that not all sellers are bad. But there are plenty of scammers around too. You should be extremely careful about who you purchase from.