The price they end up charging may be a “fair market rent”; it may not be. But it doesn’t have to be, because the couple effectively has a monopoly - on conven

The price they end up charging may be a “fair market rent”; it may not be. But it doesn’t have to be, because the couple effectively has a monopoly - on convenient parking for the houses that the residents already live in. You might argue that the street was always privately owned. But if the parking fees had existed when the residents were searching for a home, they could have factored them into the price, and if the result was too high, they could have easily picked another offer. Thus the parking fees would have effectively been part of a competitive market for housing. However, now that they already live there, moving out would have a significant financial and psychic cost. The limit on the price the couple can get away with charging is set by that (along with, of course, the perceived cost of alternate parking arrangements, again both financial and psychic) - not by anything related to the market value of the land they own.