When you buy something, the price can be set in different ways. You and the seller might agree on a specific price when you make the deal. Or, you might agree on a way to figure out the price later. Sometimes, if you've bought things from the same seller before, you might use the same pricing method you've used in the past.

If you and the seller haven't decided on a price using any of these methods, you'll need to pay a fair price for what you're buying. This means you should pay what most people would think is reasonable for that item.