verbal agreement should go both ways. But sadly, the buyer is the one usually take advantage of the seller. Seen too many buyers agree to the deal and later called back saying they find a better one.
For me, I still go by the fixed price that I advertised so if the person meet my asking price, I will not be selling to the next one who offers $10 more. And I allow reasonable time (1-2days) for the person to meet up with me to finalize the deal.