Another way to think about it is that prices come from a game where one player wants the number to be higher and the other wants it to be lower, and the players can walk away. That's a voluntary exchange.

I don't know why you think the existence of this game needs to be proven when it's a game people play all the time? It's very unlikely that you've never shopped for anything.

Not every purchase is entirely voluntary. Some purchases happen under pressure. The amount of pressure varies quite a bit.