Saw Salesman by the Maysles Brothers recently, and this sure is an american classic. I can't believe the people let themselves be filmed the way they behaved, but this is a sure reminder that society was ready for soapy "talk-shows" and "reality-shows" much earlier than the 90s.
We follow four salesman on their work selling bibles door to door, while the film builds up to a human tragedy. Life wasted, hopes crushed. This is one of the most revealing films about the late 60s in america I ever saw, and an indication of almost everything that went wrong with it. Why was there a student revolt, why did the youngsters rebel? The answer can be easily found in this film. The people have no money, no hopes, live like zombies more than anything else, and aren't able to express themselves, as constant role playing is going on. Their self-esteem is so low that they consume almost anything to try to build it up. This was a really lost generation. And the salesmen are all in the same boat. No difference between them and their clients, other than that they have a different role to play in society.
If you wondered wher David Mamet got his inspiration for his Pulitzer-prize winning play "Glengarry Glen Ross" in 1984 you won't have to lokk no further. The great 1992 film version could be regarded as a kind of remake, with Jack Lemmon taking the part of "Salesman"'s protagonist. They not only look very similar, but Lemmon in what may be his best performance in his career almost mimicked Paul Brennans traits and gestures. 
The film is a must see.