All those things you have listed (types of jobs to do, types of jobs to avoid, sourcing parts, not ordering the wrong parts, making money after paying mechanics really well) were all big challenges. It took us a while to figure those things out and now its our competitive advantage. There are still occasional problems, but we are getting better at it every day. Our model assumes that 2% of the customers will have unreasonable demands / ask for refunds etc. Happy to chat anytime art @ yourmechanic.