Hi, I'm a brand new member who just stumbled upon this forum.
I found a great price on a Marriott certificate, corresponded at length with the seller, and placed money in an account at escrow.com .
The charges were minimal, particularly compared to the amount I am saving with the certificate, and it gave us both peace of mind.
Perhaps my experience isn't typical, and it did require a bit of back and forth + verification, but it was really work an hour or two of an afternoon to save hundreds and hundreds of dollars.
YMMV.