I've found the seller are very acommadating, one of the sellers even offers a refund policy if you arent happy with the timber, can't ask fairer than that.
For me, there is no difference in buying on ebay and buying mail-order from someone like SL Hardwoods.
Ask for pictures and only buy from sellers with good feedback, and you can' go wrong.
As mentioned, i've got a nice small stash of various hardwoods that hasnt cost me a lot. I would definitly recommend it if you are after small quantities.
Buying veneers is also good on ebay, i've bought some cracking stuff on there before - really good quality.