Yeah, I've seen them advertised on ebay allot. I have a tough time believing they would be a class V boat and take the inevitable abuse that would come with running at that level over time. When they first showed up on ebay I thought it was a scam. They were selling them for $400-800 bucks and offering free shipping on a RAFT!!!
I think the easiest way would be to go through the seller's feedback and email 20-30 people to ask about what they think of the raft. Feedback alone should not be an indicator of the product. Go back to the earliest buyers. Also keep in mind, I doubt you will be talking to people who have used normal quality rafts like Hyside,Avon,Aire ect. From my limited knowledge of quality raft production, I don't see how it is possible to produce,sell and make money on a raft sold at these prices unless big corners are cut.
Bottom line, I suspect you will get what you pay for. Good luck and if you do buy one please post what you think of what you got!
example of listing: