I guess that iphone 4 with ios will be 7 because if so, no one will be able to help, that's one of the barriers that Apple has to prevent theft cases, you can only do two things and always putting you in touch with seller
1 That you say your apple id and pass
2 that the seller himself into your iCloud account from any computer and the iphone unlink your account, which you can then restore and activate apple id with you.
regards