The mission of the OTW is to support the noncommercial sharing of fanworks within fan communities.

Some transformative works do legitimately circulate in the for-profit marketplace as well: parodies such as The Wind Done Gone (the retelling of Gone With The Wind from the perspective of a slave), critical analyses that quote extensively from an original, "unauthorized guides," and other types of transformative works have long traditionally been sold.

However, these works are generally of a type which the original copyright owner would not authorize and which the courts have found should be allowed regardless of the copyright owner's consent. If you try to sell your derivative Harry Potter novel, on the other hand, you would have to make a strong case justifying your doing so without authorization from J.K. Rowling. The courts are going to be justly skeptical that you are borrowing her property for any reason other than to make yourself some cash off her characters.