I've been doing commission work for some time, and kind of disagree with ScottA (sorry guy). Ownership is important, because you never know what will "take-off" and become an extremely valuable property. With small deals (anything under $10,000 commissions) joint ownership with no exclusives is probably the easiest form to manage and protect the both of you. If your client is insisting on exclusive ownership then jack up the price to at least double what you might otherwise charge. If your client is not the one bringing up the subject, then the less said, the better - leave him to "assume" that he is buying full rights (but don't mislead or decieve him). The current copyright law is in the favor of the creator, who retains ownership and rights unless expressly transferred via a written contract -- even if you are paid for the work. If the original design is theirs, then they retain those rights anyway, and you can not use the character based on their design even if you make the mesh.