Thanks for the advice people. I had been skeptical since the beginning of the negotiations with the "buyer".Sad to hear it wasn't a legit offer, but I'm wiser because of it.
I'm about to close on a deal with a buyer offering me a pretty good amount of money, but before we proceed with the transaction the want me to send them a screenshot of my domain account (to prove I'm the legitemant owner), and a domain certification from a specific website that they linked...