True. Maybe I'm just naive, but I thought the dealer I bought my car from was decent. I lived right near a place that does non-negotiated pricing so maybe that makes a difference.
My own sales experience in selling much smaller things suggests to me that commissions are bad. I was paid by the hour, and as a consequence I consider myself to have been a fairly objective and honest salesman. There were performance incentives, but they failed, which I thought was a good thing. When the place reformed and added in more meaningful performance metrics (among other things), I left.
And I think, in general, any sort of system that attempts to tie compensation to specific performance measures is a bad idea, because it creates an incentive to game the system. The same thing happens with police departments and crime numbers, health care providers that are paid by the procedure, brokerages that charge per transaction fees, and so on.