That's the whole point of legitimate auction houses like Sothby's. They pay experts to provide some legitimacy and sanity.
It's one thing for me to say that a kids finger painting is worth 50k, it's a different thing for a trained art appraiser at an auction house to set that price.
Sotheby sets the initial prices and provides estimates of value. They were supposed to be the responsible adult in the room. Now if they values them at say $1000 and they sold for 100,000k that's on the buyer. If the value was set for 80k and it sold for 90k that's a different story.