> Apparently, this domain was owned by a seller who listed the domain under Namecheap's 'Buy Now' tool, which according to NameCheap, is only intended for fixed price, non-auction sales.

Perhaps I am an asshole, but seems like they sold their domain for $31, you bought it for $31 and that's that. Good on you to offer $3900 but for $8000 I would pay some lawyer to put them on notice.