Well if he is offering to sell it to you and if he has it in hand ask him for a photo of it transformer, even partially just so you know he has it.

As for it being starscream who could say with any certainty that it is or isn't at the moment. but it does look like his jet mode especially at the tail.

Personally I'd just wait for the store release its not that far away. But if you don't want to wait pay by paypal just to cover yourself.