That doesn't look like a fake to me. I have the one posted above sold by the Amazon seller and it is nothing like the one OP posted from eBay. The one I have is cheaply made and it is very obvious - the one on eBay definitely looks more like a real Tamagotchi. The only thing that is strange is the backing but that may be because it is another country Tamagotchi - maybe Europe considering the ball chain. The picture on the top is similar to many other Tamagotchis as seen here:
Actually, this picture has been posted somewhere on TamaTalk:
(credit to Mothra, I think this is her picture)
Anyway, these are all European Tamagotchi Plus models. The one in the upper left corner looks a lot similar to the one posted on eBay for the exception of the colors.