Let me start by saying this is still bad advice but I’ll forgive that you dont know how it works here because I have no idea how it works where you are.
In the states, there is the ASE certification. Its akin to an IT cert. There are a bunch of them. You dont need them but no reputable shop is going to hire you without that or equivalent experience. So starting out you might get to push a broom and after some time goes by you MIGHT get to do a brake job. A farm hand probably gets more mechanical experience than that. Unless you take a big interest in working on cars no shop is going to take someone in off the street. They will just be a liability.
Also mechanical stuff is a lot easier to prove to the mechanically inclined, which if those people were, they wouldnt bring their car to a shop. IT stuff is no different.
This is where you went full retard though,
Telling someone to not go into business for themselves in IT but then telling them they could do engine tuning is laughable. What do you expect would happen if someone gets their engine tuned and then they go beat the piss out of it until uncle rodney comes knockin? “uh man, I think your tune was bad.” Then he gets taken to small claims to replace the D16 in some kids 90s honda.
You seem to be stuck on the idea that this is what we’re telling him to do. We’re not. No one is. Though every business venture requires some kind of capital to make it happen, its generally understood that you would want to minimize risk. Telling someone not to go into business for themselves because of risk is like not going outside because you could get hit by a car. There are ways to mitigate the risk and if you look both ways before you cross that boundary you’ll probably be alright.
Repairing computers on CL is not a bad idea because of risk, if it was there would not be so god damn many posts in that section. Its a bad idea because of saturation. Theres likely 5-10 other people doing the same exact thing already.
Buying broken stuff, I agree, doesnt make much sense. Getting broken stuff for free and trying your hand at fixing it makes much more sense and could actually be profitable. Tools do cost money but skills are priceless. (BTW did you know in america you would have to buy your own tools to be a mechanic? shops dont provide them.)