SWEET!!! My problem is solved, thanks to David Browne - Microsoft. It doesn't show up in the answer he initially proposed, but his next comment solved it for me. Quite simply, it was a matter of turning the EF change tracker off.

context.Sales.Include(x => x.Buyer).Include(s => s.Seller).AsNoTracking().ToList();

Obviously this wouldn't solve the problem if there were to be any kind of editing done on the result, but in my scenario that's not an issue.

Thanks a lot, David!!!

(P.S. David, you should get credit for this answer, so if you want to post a different answer/explanation, I'll give it the credit it's due. :)