Arthur Miller believes that there are true and false values in the world. The chief false value he exposes is the idea that a person can—without any expertise or other skills—make "easy money" based on having a good personality.
Willy Loman can't divorce himself from the idea he can open the floodgates of wealth as a salesman. As the play opens, however, he has gotten old, and it is finally dawning on him (though he doesn't want to accept it) that riches aren't going to come his way. He isn't that good a salesman, and now he is getting washed up. He even loses his job.
Unfortunately, Willy has tried to pass his fantasyland ideas of easy money and striking it rich through personality and connections to his son Biff, which has also messed up Biff's life. Willy has discouraged Biff from working hard in school or getting more education, thinking instead that Biff could get ahead on personal charm. This has not worked, especially as Willy has inflated ideas about Biff as a stand-out person. Biff is a reasonably decent human being, but not the spectacular individual Willy wants to believe.
The true values are those Willy has missed all his life while chasing his illusions. He is, for example, good at gardening and enjoys it, he and could have made a solid career out of horticulture if he had decided to study it and accept that it would make him comfortable and happy but not rich. Biff, during the play, starts to discover that it is better to face reality about one's limitations than to try to chase wild dreams that are never going to come true.
Miller values gaining knowledge and expertise, working hard, putting aside concepts of "easy money," and being honest with oneself—all qualities Willy lacks.
One of the strongest display of false values in the drama is the idea that drives Willy in that money and material wealth is what defines success. Willy's primary motivation to be a "something" is a construction that is only measured by money and economic representation of the good. For Willy, this pursuit is one that is rooted in false values. Willy's entire conception of self is driven by a desire to appropriate the world in accordance to false values, or elements that are not lasting. Biff points this out to his father:
You were never anything but a hard-working drummer who landed in the ash can like all the rest of them! ... I'm nothing, Pop. Can't you understand that? There's no spite in it any more. I'm just what I am, that's all.
Interestingly enough, this moment reveals an instant in the drama where real values are illuminated. Miller stresses that the open and honest exchange between individuals about who we are, what we believe, and the essence of our identities form the "real values" that define being in the world. When Biff recognizes that he is what he is, "that's all," it is an instant where there is honesty and an embrace of real value. This is where the drama suggests that Willy will always come up short and fail to understand reality. Biff summarizes this in assessing his father's life as one in which he "never knew who he was," holding on "to all the wrong dreams." This honesty and courage to look life in the face and recognize it for what it is within its pain is where there is a true value emerging in the drama.