As I pointed out earlier many sellers insist that they will not replace/refund if the buyer doesn't take out insurance and I think this is fair enough. Of course it probably depends a great deal on just what you're selling - bone china is at more risk than bath-towels for instance.
If a buyer complains as you say Bartleby, and you pay them off rather than get a neg., you will at least bar that seller from bidding on your items again, presumably.
I can only speak for the field in which I operate. Perhaps there are more shifty characters in other peoples areas of interest. I can't believe there are enough buyers practising such shonky goings-on to make a severe dent in an honest sellers record, though.
What happens if we ALL decide not to post feedback first? The system breaks down and it's open slather for every dishonest operator out there! We'd all have to give it up.
GG