Yeah, there is a forum that talks about good and bad ebay sellers if you'd go farther down the forum list on the mympx.org home page or go here:
Bad sellers/Blacklist
You can also google the seller ID too because buyers who have already left positive feedback but were cheated would sometimes post their complains in forums like this and it will come up on google search. You should add your seller's name in the bad seller forum to help save others.
In general, however, there is always a risk when buying mp3/mp4 players from China off ebay. You are better off going to legit web sites that sell brand China players like Allpmp or Mp4nation.