If it is a paypal dispute and the stamps are not returned in the condition they were sent (i.e. unused) then you can tell paypal that.

I am not sure how you will go though. In the "olden days" the buyer would lose the dispute, but there is plenty of evidence that the buyer always wins now.

If it is a Not As Described dispute on the grounds of an incorrect font, could you ask him for a photo...if it is As Described you can also tell paypal this.  It may make him think twice about a dispute if you have photographic evidence that the font is correct.