I know you are kidding, but it is surprising how many people come on here thinking that they have some magic million dollar relic only to find out that their box (that near ALMOST ALWAYS looks good, but hasn't been played in 50 years "so it has to be like new", and is in reality rotting and disintegrating inside), has no real value... and more, if they wanted to get working properly, the cost to repair greatly exceeds it's value.
I can basically say that there are only 2 groups of instruments that over long periods of time hold their value:
1 - Hohner Gola (IF PROPERLY MAINTANED, greatly increases it's value)
2 - the musical instruments of famous/renown accordionists like Diero, Welk, etc... and have the provenance to prove it and condition is not even all that important, but it helps.
Now, I am NOT talking about true quality instruments, those ALWAYS will hold value to some amount if in good condition, accordions like top of the line Pigini, Excelsior, Hohner, Beltuna, Scandalli, etc.
If someone brings up their great grandmother's low/mid range damp, rotting and non-functional accordion that looks great, I cannot tell you how many times I do the full out eye-roll when they ask the value... lol