Setting up salt water tanks after you really get the hang of it is probably quite repetative. Automotive work is always changing, nothing is ever done the same way. Setups are always changing. And things will always need different work than others. There is a lot of technical work that is involved. Measurements, specs, torques, and so on.
Its not something that you just entrust to any shop. Cuz yes, probably 75% of the shops out there are there to just make money and take advantage of their customers. There is very very few trustworthy shops. This is why people are starting to work on things themselves more often.