Seig does have a valid point in regards to valid qualifications. The vast majority of Martial arts instructors do not have the qualifications or credentials to teach firearms, at least as far as there use. Retention/disarm is fine. They may know how to use a firearm, but that does not qualify or count towards valid credentials. NRA is valid and has been since it's inception. Same for Police and possibly even military. I would not be concerned about liability in and of itself. You can be 'liable' for simple taking martial arts in general if the opposing attorney decides to go that avenue.
Know the qualifications/credentials of any instructor.
Know Federal, State and local laws in regards to the possesion and use of a firearm. You have the means to take a life...take it seriously.
Know your chosen pistol/revolver/long gun.
Practice as safetly as possible the worst case senerios. Standing in a booth and shooting paper does not prepare you for the real world. Seek the most advanced, intense, realistic training that you can reasonably afford.