How do we decide how much we are willing to pay for things?

Let’s take black pearls as an example:

The interesting thing about black pearls is that when they were first introduced to the market there was essentially no way to gauge how much they were worth: were they worth more or less than white pearls? Most people instinctually believed that white pearls were still more desirable. But then the black pearl discoverers had an lucrative insight: take these unfamiliar black pearls to a famous jeweler and have them displayed next to the more precious gems: rubies, sapphires, and so on. The result still lives with us today: black pearls are now worth more than white pearls.