If you can manage to take a photo of the ray and post it here we can probably help you out with it's identity. If it is a freshwater ray, illegal in California, do not purchase it.
I'm all for legalizing illegal fish species in areas that people can't normally get them (providing the reasons for them being illegal are bogus), but if they're illegal and they're being sold I believe there should be legal consequences. I've been arrested 4 times for having something in my possession that I strongly believe should be legal, but was nonetheless illegal, so I was arrested. The law is the law, whether you agree with it or not, and it should be enforced.