nobody ever went broke underestimating the taste of the American people

Meanings

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

Etymology

Widely attributed to American author and social critic H. L. Mencken (1880–1956) but not found in his published works, so the source and original form of this expression are not known with certainty.