It's not econ, it's psychology. I wrote a column on this a while ago.
https://open.substack.com/pub/adamst...utm_medium=web
One thing most people forget when ranting about BP is the other side of the equation. A consignor with a $100K+ card to sell frequently negotiates for a chunk of the BP. The consignor may be getting 105%-115% of the hammer price if the item is good enough.