It could be
that the seller did the same research as you and came to the same conclusions as you did, selling it to you in good faith.
This might, conversely, not be the case too.

If I had ever misrepresented...
It sounds like the seller made an honest mistake.
If I sold an item which I had accidentally misrepresented, I would appreciate the buyer letting me know. So, if you are not happy with the chair, definitely contact the seller.

return policy
Josh,
Unless the receipt has the "spcifics" of the chair (the product name, designer, and manufacturer) you have no chance. The chair sounds to be an authorized reproduction made by a different firm and sold in good faith by an ignorant dealer. I would feel badly that "I" did such a poor job in looking for labels prior to the purchase. I always ask myself what it my part in this dilema.

Contract of purchase
If the item is not what the seller said it was, you have every right to return the chair for a refund. You have a verbal contract with the seller and if he/ she has not sold you the real deal, then I would think it is the seller at fault, rather than the buyer.
I think most sellers would want to know when a customer is unhappy with a purchase, as word of mouth plays a large part in this industry. Having a knowledge of vintage pieces does help when you buy, but I don't think it is the responsibility of the buyer to confirm authenticity of vintage pieces, that is the job of the seller and is why we pay a premium price when we purchase from a dealer. We are paying for his/her knowledge and reputation. That's why I only ever buy from people who will give me a receipt with confirmation of authenticity. Good dealers are generous people who will give you sound advice on buying, caring and investing in vintage furniture because they are passionate about their industry and have a reputation to uphold.
So in short, take it back if you are unhappy. Perhaps the seller can give you a refund or offer you a replacement item of equal value.

Sounds like you'll be prepared should the
possible conversation with the dealer go south. The question at this point is, "Are you happy with the purchase?" If so, no problem, no conversation necessary. If not, then things will most likely go smoothly. Doesn't sound like you've been scammed, but more likely a victim of a not-fully-informed dealer.