(though I do feel I have seen Best Offer prices list correctly when they are higher than the start price. No guarantee that is still the case or always the case. I've also seen the prices appear to come good after a couple of days).
I made an offer on a book last week 20th June (higher than starting price). It was accepted. The starting price is still showing now rather than the price it sold at.
Good to know. I guess this means the Best Offer data points are pretty much useless.