In Star Trek: The Voyage Home after dining with Gillian Taylor, Kirk excuses himself for not paying for the meal stating money does not exist in 23rd century. Years later in Star Trek: Generations Kirk and Picard meet in the Nexus. While Kirk is realizing that his experience can't be real he says the following to Picard:
Come on in. It's all right, it's my house. ...At least it used to be, I sold it years ago.
How did Kirk sell his house in absence of money?