I disagree with you. Put yourself in the sellers shoes - and recognize buyers evaporate into thin air without notice all the time. If you wanted to lock up the seller you would need to get an agreement that you wanted a period to consider it and have first right of refusal in the event he/she receives another offer.
AFAIK, all "best offer" systems work this way, where an open offer or counter does NOT lock up the seller. At least A'gon, and eBay work this way.
AFAIK, all "best offer" systems work this way, where an open offer or counter does NOT lock up the seller. At least A'gon, and eBay work this way.