Sounds like he listed the item under market and got flooded with offers. I understand taking a better offer if the first isn’t finalized. Just about anyone here would do the same. Your deal sounds like it was not accepted in full as you said you were discussing delivery options, which means things were not fully settled? How far out were you looking at for delivery? Maybe he didn’t like the delivery options or time frame, and someone offered to pick it up in an hour with a higher offer?

If buyer accepted your offer AND also agreed to pickup/deliver at exact X location at exact X time, then yes I agree you have a gripe.

But playing devils advocate, who here hasn’t passed on other offers because they were honoring the first offer, only to have the first buyer no show and you lose out on other buyers too? It makes people skittish - buyers with cash and immediate pickup start to look very attractive. In my experience if you’re buying an under market deal, you need to offer immediate pickup and cash.