I sell my products (not bath & body) at wholesale and I ask for a tax ID number when establishing a wholesale account with someone.
That information tells me the person is prepared to pay state sales tax on sales within their state. Otherwise, I could be held liable for paying MY state sales tax on my sales to them.
It also means the person is more likely to be a legit business -- it weeds out most of the retail buyers who sneakily want to buy at wholesale.
If a craft fair does not ask for ID numbers, then the fair organizers could be held liable for paying state sales tax on the gross sales from the show. So it's pretty dumb to not want that info from their vendors.