I used my old Mini Cooper (second generation version) for a minor (light) fix on my 2017 i3 with REx. He bought an i3 (2015 or 2016 version) last year to begin practical training/learning on i3's. Here is his website --- http://www.baybridgemotors.com/
They work on BMW's and Mini Coopers. Worked on mine for 17 years. He has talked me out of many (stupid) mod's which took money out of his pocket.
I would say to give him a call. I believe he would treat your fairly and honestly.
Good luck finding a good non-dealer mechanic. For now, i will go to him about my i3.
BTW, i just gave my 2002 175,000 mile Mini Cooper S to my nephew's daughter. It runs darn good and she is stoked!