It depends. For the autographed posters, we typically put them with the book they reference and put it with another age-appropriate educational item. If an author sends a signed series of books, we usually keep them together. However, if we have an autographed grouping of items that has the auction committee talking, then we will separate them into smaller baskets to raise more money. For instance, a children's author and illustrator sent 4 of his books in hardcover format to us, drawing a scene from the book and signing it on the flyleaf of each. We sold these in pairs.
We sometimes group two or three autographed books by different authors if they fall within a specific reading level or age range for interest. I wouldn't group more than 3 books together, though, unless it is a series.
Guess the short answer remains - it depends. You'll find out what works for your audience after reviewing the results of the first auction or two.
