Here's an idea

Last week, in my item about the Unionville High School's annual used book sale, I said that I no longer go on Friday nights because of the large contingent of book dealers. I used the euphemism "motivated" to describe their behavior.
One of my readers agrees: "The “motivated dealer” problem has gotten worse. I do not cast aspersions on all the dealers, but the sight of one who just tossed all of her “rejects” onto a pile, rendering the neat rows a complete mess, was just sickening. And, as you said, it is difficult to casually browse when great swaths of books are blocked by the dealer, his or her helper, and all of the boxes used to carry the books out. They are intent, on a mission, and could care less about we mere book seekers."
Nonetheless, he and his wife go on Friday anyway because "I guess we are afraid that someone will snatch that one (actually many) volume(s) that just must be added to the library.  In my case books about Jack the Ripper (a fascinating factual recounting), Stonehenge, and nature essays among others."
He asked: "Has any thought been given to giving dealers their own time slot?"
This seems to be to be an excellent idea. The dealers, and any other dedicated collectors like my friend, could be charged a premium to come in early for their own "golden hour." Then they, with their boxes and carts, could be shooed out and we regular, not-in-it-for-a-profit folk could take over. 
Then again, the book sale is always run by pretty smart people; perhaps they've thought of this, discussed it and decided it wouldn't work logistically.