It wasn't uncommon to come in at 7 AM and close up at 11 PM after dealing with idiots that demanded to drive 5 cars and then get kicked out because they had 350 FICOs and wanted a new SUV with 0 down. The majority of people had no idea what kind of car they needed or what they could afford.
The things this guy doesn't point out is that dealerships will work with banks to get deals financed that otherwise might not be, they provide loaner cars, make sure people have insurance, and they deal with title/registration paperwork that is a huge hassle. They'll also take just about any trade-in if it runs (and some that barely run) and dispose of them (something that could cost you).
Vehicles are the highest value or 2nd highest value purchase for most people. You definitely need to know your stuff when purchasing a car, and I'm totally against predatory dealership tactics, but after working in the industry I don't have faith that the average american can navigate the myriad of vehicles, processes, paperwork, and other tasks that go into buying/selling cars directly. I also have a hard time trusting an individual seller after seeing the completely wasted cars we took in on trades.