You would hope a new vendor would look into how the payment system operated, it could be a complete case of naivety or it could be something more sinister. They haven't technically done anything wrong at this stage though as they didn't ask you to finalize, well not directly anyway. Best thing to do is post a warning on the forums to alert other potential buyers to this and see if anyone else had a similar experience because if it happened to a lot of people that would suggest the vendor knew exactly whet they were doing.