The used bike market is an odd market.
Is a 10 yr old bike truly worth next to nothing... especially if it has been ridden infrequently and well cared for?
What if a similar model is still being made and sold, at more than the original price?

Can one upgrade the bike, for example replace Claris 8s with Ultegra 11s (doing a thorough and good job)... Then what is it worth?

And what if the parts are worth significantly more than the whole?

There also seems to be a great convergence in prices. So, a $200 bike might drop down to $100, but a $1000 bike might drop down to $200 or $300.