Plan and Book Your Vacations. This link is to an anthology of resources for the collector. Visit their web site for additional resources. Sometimes an artist with limited facilities made something in very small numbers. Sometimes a piece is rare because it did not sell well, so few were made.
Breakage also cause rarity.
It could also be something that few people save, like gum wrappers or trolley-car ads. Prices have actually dropped for some book titles. Buy what you like or what you can use, or buy something because it reminds you of some part of your family history. An option for sellers in which the closing time of the auction is extended for a period of time if the bid is made within the closing minutes of the auction. The process of finding the maximum bid of a lots current high bidder.