AC - I may not know much about how porn sites are run, but I do know a little on how graphic artists and their clients do business. What's typically done is a contract is drawn up with an agreed amount of money, the client(you)provides exact specifications of what is expected from the artist. Sometimes a mockup is done and also revisions are part of the contract until the client is satisfied. The artist will ask for a per project amount or more typically a per hour charge. I believe your unprofessional attitude and lack of experience in dealing with graphic artists might tend to rub people the wrong way. Hopefully the person you find to do this job has enough sense to go through all the proper steps of negotiation so there won't be any surprises (or court cases) involved.