Occasionally, young Illustrators will be asked to do a piece “On spec”. Know these words and fear, young padawan. For on “spec is one of the slimiest things an Art director can do.
On Spec is when companies ask for a finished piece before they wil pay you. No assurance of payment, no contract. You create and then *maybe* they pay you. Would this work with a plumber? They fix a leak and then you decide if you should pay them? Hell no. The comics and movie industry is famous for On Spec deals, since they are mostly made of evil demons.
Should you never do On spec work? Well, if they are offering a few thousand dollars, you might consider it. But it’s a shady, underhanded practice to begin with and not one a professional illustrator should enter into lightly.