Fun thread. First cash "in hand" wins the sale. Sometimes with multiple inquiries, I'll let the possible buyer know where they are in a queue. My reasoning is that they are not then under the impression that they are the only one expressing interest.
This past week I saw two CJ pieces (2550, 16LS2) come and go within two days or so. If you really want a thing it pays to be watching and to be ready with cash. Just saying.