Having been on the receiving end of client's greed (read: dickery) in the early stages of my career, and hearing about it far too often from other young artists/designers, I would like to take a moment here to explain a crucial element of doing art or design as a business - protect your rights!
Experience has unfortunately taught me the necessity of protecting your rights to your art. I had naively assumed that when you work with clients and produce art for them, you would have the right to at least display in your portfolio that you actually made that art, even if you don’t have the rights to resell it. It’s sad that this even needs stipulation in the form of a legal document, but it does.
As an artist, what other currency do you have for attracting customers other than visual evidence of your visual products? Could you imagine trying to win over a client by explaining, “Oh, no, uh, I don’t have any work to show you, but, trust me, I’m really good, you’ll see!” <–That don’t cut it.
Soooo, you need to make sure that BEFORE you put pen to paper on any sort of agreement with a client that is asking you to make a work of art, that you have had them sign an agreement or included a clause protecting you to your rights to display the artwork that you will make for them. And if they won't do that, DON'T WORK WITH THEM. I don't care how large or small the project - if someone comes to you and wants to completely own your work, including the sole right to display it, you had better be paid handsomely for it. The client stands to profit many times over the salary/hourly rate they pay you to create the work, and if you are not going to be able to build on that with other clients or similar work, demand a larger cut from them. Trust me, that extra pay will come in handy as you struggle to find your next gig without something to show for your previous efforts.
Do your research and see how your craft handles client agreements. I’ve found one standard form that I think is a great starting point - I hope this will help others navigate through those first rough waters when they set out on a successful career in the art world.