Also, I don't think it makes sense to say that you can be forced to value anything.
You can in the context of that conversation, where it was decided that values would be considered revealed through action rather than stated intention. If your action is forced, then so is your value (even though your stated value or your value revealed in the absence of coercion are/would be different)..
...So if you're not allowed to sell your trumpet, you've been revealed as valuing your trumpet more?
Available in PDF here, the short story in question may appeal to LW readers for its approach of viewing more things than are customary in handy economic terms, and is a fine piece of fiction to boot. The moneychanger protagonist gets out of several sticky situations by making desperate efforts, deploying the concepts of markets, revealed preferences, and wealth generation as he goes.