My wife's friend used to make a habit of offering to pay people on CraigsList cash for things, and then showing up with 10%-15% less cash than she committed to. Usually people were annoyed but eager enough to get rid of the thing that they sold to her anyway to avoid the hassle of posting it again. But it was scummy.

I've had people do this to me. It irritates me so much that I tell them 'your loss'. Someone offered to go get the rest and I called them out on this scummy practice and moved on with my life.

I've had tons of people do this to me, too - in fact, I am guilty of having done it (like when people ask for a $50 multiple knowing full well that ATMS only dispense $20 bills and I'm short on time to be able to break a $20).

As the seller, though, you should know that they value their time enough to at least be present, so they obviously want the item enough. You've got enough leverage to be able to tell the buyer who does that 'No'. I've said and had that said to me in those occasions.

Yup, the complainers on the sell-side should accede that roughly half the value derived from a sold item is out-of-sight-out-of-mind.