I was scouring through ads looking for work back in 2002, and came upon an ad looking for a Concept Designer. In this ad, it specifically asked for designs for a number of things, including a domed city in a desert. I spent several days working on these various environment concept designs, and sent them out to this company.
I got a call back from the person in charge, who told me how much he really liked what I did, and would absolutely want me as a part of the development team for whatever video game that was being produced at that time.
One catch: all my work was going to have to be on 'spec', and I would be paid on the 'back end'. To be clear, when someone asks you about this, this PLAINLY means that they want you to work for FREE.
They have no money to pay anyone. More likely they have money, but they just want free work from you so they can lay claim to ownership of the designs you did (because you "worked" for them on their project). They also have no business model with which they can demonstrate to you that if you do the concept design work for them, once they sell 'X'-amount of units of said product, you would then get 'X'-amount of dollars for it.
These are hard lessons to learn...
