Do not criticize others if you have similar weaknesses yourself.

Alternative form of nobody ever went broke underestimating the taste of the American people

Americans, as a group, are not especially intelligent and can be readily entertained or fooled to produce financial benefit for someone.

Americans, as a group, do not have good taste or sophistication and can be easily amused or distracted to produce financial benefit for someone.

Alternative form of people who live in glass houses shouldn't throw stones

Alternative form of nobody ever went broke underestimating the taste of the American people