Knock on wood, 99% pf anything I have bought on ebay, poster, or otherwise, has been just fine. Good packaging, sellers who are communicative and willing to be helpful and the items were as described.
As Rich said, there are the sheisters there, that's for sure, but if one knows what they are looking for, does some due diligence and investigative work before pulling the trigger, things can also be a more thumbs up experience, for both buyer and seller.