If you signed the return as a paid preparer, you can let the client know that you intend to write to the IRS to say that you were NOT paid, and to please remove your name and PTIN from any return filed by: (Insert clients and forms and Tax IDs).

You could also file a claim for theft, but generally this is not recommended, as the cost of filing, etc. is greater than any possible return. Chalk this one up to a "learning experience." Where you don't know the client, returns must be paid before you give the client the completed tax forms.

For the future, you need an engagement letter which the client should sign BEFORE you do the work. This includes your rates and possibly an estimated cost of preparing returns. There is usually a lot more in an engagement letter but it functions as a contract.

For new clients, you can also ask for a retainer which would at least cover your out of pocket fees. If you lose any potential clients, this would be better than being stiffed.