This. Of value to whom, for what purpose they might have, for a given time.... and given the "value" of currency at any given moment. The price at which a market clears is a reasonable fixing of the value, given all of the variables. Even then the assessment of value isn't the same for either side of a trade: the consumer considers the product to be worth more than the money paid and the producer considers the money worth more than the product: they don't agree on the value of the product. If they do... one or the other is an idiot for making the trade.

A Picasso can sell at a lot of money because not because of the labor put into it, the materials it's made of, etc. It sells for a lot of money because to someone believes it's worth it.