Why not list in your email "agreement to purchase" some rules which you expect both of you to abide by? Payment must be recieved by xxx, or postmarked by xxx, etc.? This is basically what people do on eBay in the text of their auction. Then, if the cash doesn't arrive by that day, your ad is still valid.
Non-Buying Buyers-check's in the mail? Yeah Right
It's amazing how often "buyers" tie up your item promising to "buy" but payment never arrives. They don't reply to emails. Maybe they have a similar item to sell or just like to "have fun" with you. But who cares why.We should come down hard on them. Be great have a way to post negative feedback for these NON-BUYING BUYERS or better yet, ban them. yours thoughts....