I fix lots of things and there is no experience like doing something, there is also this weird cross-pollination thing going where knowledge acquired in one domain helps you in another. So while I am well aware that most of my repair jobs are net negative in terms of actual material value generation for me, the gradual increase in my capabilities in many different domains ends up helping me even in my chosen specialisation. By this point I am just generally at an advanced beginner stage of anything after some basic research (which I have naturally becomes quite good at).

There is also a skin in the game effect that even a paid random plumber is not actually that invested in doing a good job and, while you cannot compete in terms of speed of executing a fix, or possession of special tools, you can compete - and exceed - on final quality simply because you really care about the final outcome.