When I was rebuilding my ‘54 I needed cash , so I (reluctantly) liquidated a bunch of firearms. Armslist was still a viable resource at the time , used it like marketplace. Sales were brisk. On more than 1 occasion , in the interim between making a tentative deal over the phone and meeting with that buyer , I had individuals contact me and make a higher offer. In each of those occasions I told that person that I was obliged to follow through on the tentative agreement , and I’d contact them after. In each of those occasions the tentative deal was consummated , I told the tentative buyer that I had someone else waiting in line but did not use that to leverage the agreed upon price , and I contacted the standby guy to inform him that the item was no longer available.

That is the only way to conduct a transaction , unless , of course , a seller has no personal integrity.
It seems that personal integrity is diminishing in today’s society , along with situational awareness.