I have to agree here, contract law is going to be more straight forward than trying to deal with use of the DMCA. You could probably use it after the fact, but

I have to agree here, contract law is going to be more straight forward than trying to deal with use of the DMCA. You could probably use it after the fact, but you would still be better to argue your case for a verbal contract. You can prove ownership, the business can prove payment if they have made any. The trick on a verbal contract will be proving the meeting of the minds that you had an agreed upon number and that that number was not paid to you. If you receive 50% up front the other party could argue that, that amount was the agreed to amount. In a situation like that it is almost better to not be paid at all, because you can prove that their was no consideration and therefore no meeting of the minds. Remember something in writing, no matter how crappy it is, is better than nothing in writing. Even if it is: I am going to build an application for X and X will pay me Y the ownership of the software will transfer to X when Y is paid in full.