I just noticed this.

If you were not under a works for hire agreement, i.e. if there was no specific clause in any contract you signed with this client under which the intellectual property generated by you belongs to him, then you own the copyright on the FLA and code automatically. He owns what he paid for: A final product in the form of an SWF file.

Unless you specifically stated in writing, e.g. a contract or distribution license, that he had to pay for use on a per-license level, he is allowed to decompile that SWF, and modify it for other machines. He is allowed to use it for any purpose and alter it to suit his needs. He is not allowed to sell the code. He does not own the source or rights to the source.

It's too bad you gave him the FLA, but even so, at this point you would have legal remedy if he tried to resell the code. If there's any hint that he might be doing that, I would hire a lawyer immediately and go after him.

Oh, and work hourly. A 12-hour job should never turn into 100 hours without you getting paid for it, especially if you're as good as you say you are. If you aren't going to work hourly, always have a written contract stating the exact parameters of the job being paid for. And don't let them insert the works-for-hire clause because then you literally can't reuse your own code in future projects without risking a lawsuit.