Very interesting. I am in Massachusetts. I worked in an auto body shop for several years growing up. Parts markup for auto body work is 0% in Massachusetts. The insurance companies have books that list cost of parts, and labor times to repair/replace. You don't get any more, and you might get less because of overlap. The labor rate paid by insurance companies is fixed here, too.

For mechanics or other non-insurance work, they can charge what they want, but their prices always end up below retail. If there is markup, it isn't much. It costs me less money to pay someone to change my oil than it would if I bought the oil and filter myself.