What Makes Someone An Art “expert” To Determine The Quality And Meaningfulness Of A Work Of Art?

Isn’t all art and beauty in the eye of the beholder? If I think Magritte, Dix, Van Gogh, Monet, and Raphael are great and Harring, Pollock, and Warhol are totally over-rated, how is my opinion worth any less than someone who has taken lots of art appreciating and art history classes?
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Who gets to determine what is great and important art and what isn’t?