The one thing I'm not hearing here is SAFETY. Independants and fly by nights aren't given passwords or the equipment to calibrate because they are NOT properly trained, these are failsafes to protect the customers investment the operators running them and the mechanics working on them.
You get what you pay for, if you allow an untrained mechanic to work on your BMW and it takes twice as long as a factory tech what have you saved and worse what if he fry's it and then you have to pay the dealer to fix his screw up which will likley cost twice of what it should have origionally cost at the dealer.

anyway i'm rambling now but I think I've made my point.

Have a safe day.