Is modern art a fraud?

Is modern art a fraud?

How do we know that a painter who devotes  their afforts to modern art is deceiving us?
When do we know we are in front of a good picture or a bad one?.

We know by History that many pictures have been sponsored by the mentors of the artists who painted them. For example, Guggenheim and David Rockefeller were sick to death of the social artists of the 30´s like Diego Rivera or the German expressionists and made famous and valued abstract painters who did not give them any troubles such as Jackson Pollock.

Who decides what  a good or a bad painting is? Can we go back to the figurative art? Is a video -recorded performance of a artistic value or is it a leg-pull? What do you think about all of this?