The magic of money is that it makes the incomparable, comparable. If you can put a price on something. The impossible question of what something is 'worth' to you becomes irrelevant. Price is a clearing mechanism. It just needs two people with something to swap, and a price they are willing to swap it at. You have a willing seller if they believe the thing, whatever the thing is, to be worth less to them than the price. A willing buyer believes the thing is worth more to them than the price. They can both be right, because value is personal. So trade is win-win since there is more value afterwards than before, even if you can't count value. The key is willing buyer, willing seller. Markets fall apart when either of the parties is forced into the exchange. Rule #1 of successfully engaging with the world of money is never be a forced buyer or seller. Make sure one of your options is to walk away.
It's not trade if there are chains