Anybody can get sued for anything
I am not an expert but I am pretty sure you are exposing yourself to potential personal liability (house, savings, etc) if you advertise, and charge for service and if the service proves faulty and there an injury. all it takes is one instance to put you into a bad place
If you are advertising, you have a business and technically you need a business license
I know a local charity I work with has a double/triple check system to ensure volunteers work is checked by a certified mechanic
__________________
Life is too short not to ride the best bike you have, as much as you can.