I think he is implying that installers at Best Buy are not very good at what they do.
The reality is, well, different. I knew some people who eon's ago, while in HS and College, works at Best Buy as installers and they were very good. Best Buy pays for training and you get the hang of it.
But... lets be honest, any time you pay someone to work on YOUR property you take a risk. Ownership builds concern, and if you don't own something, you don't care. This is true of all forms of property. People destroy rental cars while babying their own. The difference psychologically between home ownership and rental is immense.
I digress. The point. You are paying some person to install a head unit. Have you ever done that? It is a pain in the bed, regardless. It seems more and more complex every year. Newer cars are just so damn complex... you have to spend an hour of fine, detailed work, to even get the dash off to get to the bay.
Imagine doing this.. all day.. every day.. to cars that you don't actually care about. I don't care if you are a local or chain installer. At some point you are bound to have people who have a bad day or bad night and just DO NOT care.