I probably need to quit on this post. It is a perspective that I am trying to give. I am not trying to change your opinion, nor am I getting upset. I didn't figure my words would stand well within the DIY section.
The fact that many have found techs that either don't care or are swayed by being a good guy into doing such poor business practices does not make the practice any more acceptable. The efficient repair is always done with me, the tech, providing the parts for many reasons. The comparisons to the computer industry or the real estate industry are inappropriate. A more appropriate comparison would be with the Medical industry where skilled practicioners would never think of letting you bring your own medicine.
Bosch Master, ASE Master, L1
33 years MB technician