One solution to deciding how much an asset is worth is to let you declare any value you want for it, with the caveat that if someone is willing to pay you more than the declared value, you must sell it to them.
Now obviously things like transaction fees need to be factored in, and timing should matter - you should have the option to increase your stated value if something changes (or even to say "yes, okay, it's really worth X" and keep the item at the higher valuation).
That's very open to malicious actors though. Suppose you set a fair market value on your house or car. If I'm evil it may be worth a small loss on my part to 'out-bid' you simply to take that asset away from you by force, perhaps at a very disruptive time.
It also has all the other problems with estimating the true value of an asset.
Now obviously things like transaction fees need to be factored in, and timing should matter - you should have the option to increase your stated value if something changes (or even to say "yes, okay, it's really worth X" and keep the item at the higher valuation).