Linda,
While it is interesting and sometimes informative to know what is "customary", I'd encourage you to focus on what makes common sense and provides you a risk free transaction. A transaction in which another party has either of:
a) your signature on any actual conveyance document or
b) a document containing a promise of delivery (of a conveyance)
amounts to either a free option to the buyer, or, the downright exposure to you of non payment. You may be dealing with Jesus himself, but I'd still exchange goods for cash - doubly important if this is any significant amount of $$.