Why is my repair shop busy but not profitable?

Usually one of three things. Your effective hourly rate is below your cost per bench hour, so more volume simply loses money faster. Parts markup is too thin to cover the handling, warranty risk and dead stock that come with stocking parts. Or re-dos and warranty returns are consuming paid hours that never get invoiced — a 10% re-do rate silently removes 10% of your capacity. The calculator on this page separates the first two; the pricing sanity check covers the third.