Many many years ago this short stocky guy came into my shop. He opened up a gun case and inside it was a FAL. He asked me if I had a magazine for it. Looked at it and sure enough it had the selector switch. Told him it was illegal to have and I went into the house after telling him to just leave it and I would take care of it for him. He left and took it with him but I got his license number. Phoned ATF in San Francisco and told them what happened. A month later a ATF agent I knew very well came in and told me I did the right thing. Apparently they were setting me up. The head hauncho at that time was a real Pr--k. Good lesson learned though.
