Before you agree to ANYTHING, check the laws of both localities involved. I believe in California, you will need to get a permit to sell high capacity mags, and even then, they may only be sold to folks OUT-OF-STATE. None may be shipped TO California, other than to FFL holders for sales to Law Enforcement Officers only. Other states will have other laws. Make sure you know the laws and regulations in your state, as well as the state to which you will ship. If you let us know where you are located, you may get more specific info.
-John