Generally no.
Usually when you file SNAD and choose the "not authentic" option, the seller can choose to accept the return (and has to provide a prepaid shipping label), issue a partial refund or try to work with you.
If you and the seller can't come to an agreement, one of you would ask ebay to step in to resolve and more often than not, ebay decides in favor of the buyer.
However there have been cases where buyers may have to supply professional documentation proving the item is fake. If the seller knows that it's authentic and believes you (as buyer) are mistaken, they could (conceivably) force the issue.
May I ask how you know you got a fake? (The reason I ask is because I don't see where you requested any authentications and confirmed that your suspicions are correct.)