If you get a business license, make it a business like centerflank said. Go all out and make it work for you. Make sure it is sales and not operation. That is a different license in most places.

I got a warning like that before about cars. I did a lot of flipping for fun because I liked the cars and did not want to see them taken to the junk yard. I went and told them it was a hobby. They asked how I could prove it. I told them they same way they could prove it was a business, there is none. Some states count title transfers, they did not and there was no magic # to be a dealer.

Car repair was not what I did full time day to day so this was a hobby tied to my racing. They ended up taking my word on it. They left me alone and I was also able to see the info about the "complaint." It was a "friend" that I had helped many times. I did not help him any longer and he avoided me. I did not even have to say anything to him. I was not going to save somebody $100 hr on their car working on it for free if they were going to stab me and there was no way I could charge for it as a hobby.