There is a journal set up for lawyers who are involved in protection of an artists work. Their main purpose is to protect their clients from copyright infringement, particularly in gray areas.
Usually the law favors the person creating the artwork. In order to release the obligation of the law, a contract has to be set up where the buyer is protected by limiting what is required of him. The seller (the artist) has to agree to these limitations.
For example, if you are a photographer and you take a picture of something and someone likes it enough to buy it, technically the selling price ought to be the end of the buyers obligation of the artist agrees to it. That's why the buyer usually gets a contract set up. A bill of sale can act as a contract in many cases.
Fair value talks about limitations that are quite legal. You are not given any sort of expanded definition or example, but B is the closest answer to what you are given.
