Keep in mind, a cameraman was always present
'Salesman' was an intriguing, often intense film that benefited preponderantly from its true-to-life form. Neither the salespeople nor the customers were actors. I have to ask myself, however, did the presence of the film crew interfere with anything? Were we really seeing people in their unadulterated, natural state? For example, we got to ride in the car with one of the salesmen. He started singing "If I Were a Rich Man" and lamented out loud about his situation. It was easy to forget that a man operating a clumsy camera was in his face riding shotgun. Also, when people were being pushed by the salesmen to make a purchase, sure, it may have felt like we were eavesdropping on a private, pivotal circumstance, but truth be told, the living room was housing a film crew (as skeletal as it may have been). The same was true when we saw the disgruntled men in the tiny motel rooms. Half the room was being occupied by one or more of the Maysles. When a salesman knocked on a door and was let in, it was hardly as instantaneous as it appeared that the conversation began. The people had to agree to let both the salesman and the cameraman/crew inside, things had to get set up, and it had to be explained to these potential customers that a film was being made. This was NOT 'Candid Camera'. I'm not saying that the film didn't work--it did. It made the point better than any acted film could have. It just has to be taken with a tiny grain of salt for the aforementioned reasons.
He who conquers himself is mightier than he who conquers a city.