Huh? Can anyone prove a piece of art is good? Good by what standard? I am not sure I could prove I like any particular piece of art. I may like something, but if I tell you I do, can I prove that I mean it? possibly I am saying it just because everyone else does, and I don't wish to appear unsophisticated.
I can know without a doubt what I like, but I can't prove it to anyone, they'll just have to take me at my word.