Would it be a full time course or would you work part time to fund the course?
$13,000 is a steep fee (in my opinion), since you've been repairing technology in the past, have you considered 'interning' or part time work at say somewhere that does repair things?
It might be a minimum wage job or close to that but you would learn a hell of a lot and it actually gives you direct income whereas the course cost is significant and makes no guarantee that it will result in you finishing as a competent technician. If you intention is to work as an engineer (designing things) then a degree is helpful, especially in getting the first job. But it sounds like you don't want to do that, so I would question the need for a degree, especially if you intend to be self employed.
One thing to consider about electronics repair is that, especially at the mobile level, it can be incredibly fiddly. You want to do it until you are retired, but will you be able to swap an 0402 with shaky hands at 65? That needs to be considered, as an engineer as long as your brain is sharp you can typically still do your job, but if you work primarily in the physical world, it will be more of a challenge.
Your concerns over liability are resolved by both having professional indemnity insurance and by giving your customer appropriate written disclaimers that repairs are attempted on an as-is basis (perhaps fee free if you can't do the job, but you don't accept liability for that.)