One way to deal with this in the future is to state clearly that a portion of the down payment, say $100 or $200 is a non refundable option to purchase and that options time frame is good for _____ maybe 3 weeks. This will send tire kickers running, but serious buyers won't flinch.
ALWAYS put these things in writing!!! It can be inked on the back of a business card, but write it down in their presence and remind them when the time frame will end, a week or so in advance.
It is reasonable to have what I call "skin in the game" if you want to tie up someone else's asset. No skin, or cash as it were, then there is nothing to keep the buyer from dragging his feet or bailing out when he gets tired of the chase.
