"The only thing you got in this world is what you can sell"

Basically what charlie probably means when he tells Willie "the only thing you got in this world is what you can sell" meaning by him being a salesman with the careless people surrounding him and his world crashing down, the talent of being a salesman is all that he has left. The reflection of the Americans in the 1940's and 2012 aren't that much different its the same attitudes and thoughts going around today as it did back then. Work ethics in the 1940's may have been a little better as opposed to today's time.