The items concerned have been going for quite high prices and all the bidders are private listings. It's impossible to tell how many buyers are involved but it looks that a bidding war is going on.
If any one wants to keep an eye out for items like this, they are listed under
Collectables > Paper & Ephemera > Local Interest/ Topographical
I only receive emails about towns I'm interested in but I usually place messages about them on the relevant rootsweb mailing list.
Margaret