In the future, only one person will have money. No one else will be able to sell anything.
Who is this person? One person will get the patent for the uber-nanotech machine - able to take any raw input and, manufacturing at the atomic or even sub-atomic level, provide any finished output. Food, clothing, houses, appliances... all these products can be programmed in and produced. No one else will be able to sell goods because everyone else will be able to produce whatever they want on the UNT (uber-nanotech) machine.
So, this one person will have money from the patent royalties while everything else falls into the category of pirate-ware. The problem is, no one else will be interested in money. They won't need it.