A good mechanic can do the most with the least, and therefore will work on anything equally, whether the bike is top of the line or chain store. The client is the most important component, because the bike is nothing but decoration without them to ride it.
Your tools should feel natural in your hands, and your eyes should be on what you are doing with your hands feeling the job through the tools.
I like to build my workshop around me as I take on new tasks, and regularly spend an hour or two looking around places like DIY stores, handling the tools, brackets and stuff to imagine how I could build special tools from then. I buy the deadest bikes I can that has the parts I want to work on, because with them we have the least fear of getting it wrong.