Even if you provide irrefutable proof, most pawnshop owners won't care. They're there for one purpose: to put the screws to customers. I'm not talking ignorance here, I'm talking intentionally trying to rip people off. He was probably more angry that you caught the fake than anything else.
For example, there's a Rogue 6 string bass here in Suffolk VA at a pawn shop for $950. That is not a typo. Here's the link for a new one:
http://bass-guitars.musiciansfriend....ass?sku=519246
All that being said, congrats for catching the fake, and thanks for reminding everybody that we all need to be more vigilant.