That said, how could the buyer scam the seller out of $500 when the deal is calling for the buyer to pay an extra $500 which would then be returned later?
In the Op's first sentence of the first post he said,"A potential
buyer for our Marriott Newport Coast Villas has asked for a
$500 cashback." And the title of the thread is "Buyer Asks for Cash Back Deal...
Scam?" So it appears that the OP is wondering if this is some sort of a scam. As we TUGgers have seen on these boards for years now, scammers are coming up with more and more creative ways of scamming owners.
So while it's possible that the so-called buyer is trying to sidestep the ROFR, it's also possible that he is somehow, in a new and creative way, trying to scam an owner with a new method. So most on this thread are trying to determine what the so-called buyer's motive is for this shady-looking deal.
Regardless, I think the OP is being wise by not going ahead with this deal. There seems a lot fishy about it.