While I don't know your details, after spending most of my life in retail, and most of that time in the hobby business, if your employment at the shop in question is like most positions in the hobby business, the wages are likely very low, probably pretty close to minimum wage, and if it is part time there are no benefits as well. All of the jobs I had in the hobby business did come with one benefit though, and that was an employee discount, at most places dealer cost, or at least cost plus 10%. If your boss is too greedy to offer you a similar courtesy, then you are wasting your time with him, he obviously doesn't appreciate you or your talents. From your description of the situation, it also sounds like he doesn't appreciate his customer's business either, and may not be in business very long. However, the owners attitude is apparently not unique in this business.
I know a couple of retired guys who went through factory training school to be authorized repair techs for one of the bigger train companies. They went to the "school" in another state at their own expense for travel, lodging, food, etc. for about a week, and they were told by the person running the training program that the company did not pay for any labor on warranty repairs, but would replace defective parts at no charge, provided the parts were sent back first (presumably the tech paid the shipping), and the service manager approved the exchange. They asked about factory repair manuals, flat rate books for labor, factory tech bulletins for known issues, etc. and were told there were none of these things available, because "hey, these are just toys".
Why would anyone want to be a warranty repair tech under conditions like that? Perhaps you truly enjoy your work in the hobby shop, and if that's the case, fine. However, you need to understand that you will not likely change the owner's attitudes, and that it's very likely that the conflict between your business attitudes and his will probably eventually eliminate all the "fun" you derive from your employment there.
Good Luck,
Bill in FtL