[tdrdt]

"then what does it care for"

Wel most of the time it's an investment. So for those bidders the perceived market value is very important.

But you can also imagine this scenario: someone has a ring from a great great grantparent. The market value of the ring is $10. But the owner would only sell it for $100000. Then their would noone to bid against.

[HPsquared]

The ring example is interesting: if nobody actually buys it for $100000 (the best anyone else would pay is $10), then what is the 'real' value of the ring?

The only logically consistent answer is that value is always relative and subjective; 'objective' economic value is only an abstraction.