haris1 - I would send the seller a message and let him (or her) know that you assumed that the box and gun (serial number) matched and wouldn't have bid on the gun had you known otherwise. Is there anything we can do to remedy this situation.
You really do have to be polite regardless of whether or not the seller conveniently
blurred the picture - he (or she) is in the driver's seat - period.
On the bright side - you learned a lesson and shared it with everyone here. Let us know how it goes.