It's places like reverb that cause this
One person (like our German friend with guitar bodies) lists an item at x, lots of people see that it's listed at that price and assume that's the value- despite it not selling in some case for months or years.
Things seem to appear like busses. One comes up for sale, and then all of a sudden there's now 5 - all at similar prices.
Capitalism I 'spose
Fundamentally - as had been said many times over - it's only worth what someone will pay for it