I think the store owner was well within his right to protect his own interests, and that choosing not to fulfill his customer's sense of self-entitlement was in no way indicative of poor customer service.
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That having been said, I think the OP completely overreacted. I get it, the store owner didn't respond in the way that was most ideal for you.
I disagree. If the store doesn't have a return policy that allows for unopened product to be returned within 3 days with a receipt - especially if the customer intends to opt for other product - then the store may have a legal right (I don't know), but it's contrary to commonplace business practice.
I'm guessing the store manager didn't realize he was returning a product. I'd hazard that the manager thought that he was trying to sell the owner inventory. Once he realized what was trying to legitimately return product, he immediately complied, as would be commonplace business practice.