Update: Took the seller to civil court, and lost even though we agreed on the sale price, and I had a written appraisal from a music store stating it wasn't what he said it was.
Soooo.... make sure you always make a bill of sale on used items. When you buy a used item via a verbal agreement it is considered a binding "as is" contract, and there is nothing you can do. Had I had a bill of sale, the contract would have been null and void as it wasn't a Gibson, and was indeed an Epiphone.
Hopefully this will help protect people from making the same mistake I did.
Sorry to hear about that. The good news is you didn't pay Gibson money for an Epi bass.
You should post the seller's name here so others won't fall prey.