I have always had great success (luck?) dealing through real
estate agents. But I choose them carefully. For every deal
that I've done, I feel that I came out ahead having an agent
on my side.
I presume that you have a contract with your buyer that
nails down all the terms & conditions? If not then your
buyer could be continuing the negotiation all the way to the
closing table.
If this deal goes though, who is doing the closing? A title
company? Attorney? They should be able to help you with
problems.