Beethoven as a beginner was told to never pick up an instrument again. I could name countless examples of this, and so could you. The point is, no matter how bad the art is at the time you see it, the artist may be quite good. You and them just don't see it yet. The same is true for the writer, the musician, and your favorite individual working at their career.
Mercy is due here.
Kindness, rather than frankness. Yes we are judges of Art and Beauty. We are the supreme judges of all life, -but we are not its critics. Sometimes, we are not the best judges of our fellow creators and artists, regardless of their craft or trade. Someone else might like it better, and you should probably tell them that, if you do not like it yourself.