Isn't this what tags are for? Maybe this could be made more clear in the user interface, but you can search in a seller's store for any term (fiction, paperback, etc.) and any books the seller has tagged with that term will come up. The tags they've used are also in the "filters" section, so you can search that way too.

Maybe making a seller's tags appear on their store page right below the search bar (in the same way they appear toward the bottom of a book listing) would be a good way to make this more prominent. Though you would probably want clicking on the tag to display only those books from that seller, and not all books across Pango.

Yes! I’d like to be able to search a seller’s books by category grouping so that I don’t have to scroll endlessly through every book they have—and I’d like to be able to set my own shop up to do the same. A buyer interested in detective fiction doesn’t want to scroll through my sheet music and cookbooks in order to find another Harry Bosch or Lucas Davenport book.

As an old librarian, this inability to organize my “shelves” for potential customers is driving me bonkers.

Also—I’d like to be able to offer discounts on certain sections of my shelves. For instance, if memoirs or horror or romance aren’t moving, I’d like to be able to put just those genres on sale.