On all other selling platforms it is the seller's responsibilty to up to the point of delivery regardless of insurance. Ive been on eBay for 24 years 2000+ transactions and have 300+ transactions on Reverb in the last 2 years. I've seen and experienced it all from both sides. The seller is being an asshole because he knows there's no way for you to get the money back without his approval. If he doesnt give it back I would post his info so no one else has to deal with this person.