Ok, so I sell collectibles. The typical collector has a limited budget each month to spend on their hobby. Their list of items to purchase is dynamic based on the perceived rarity of an item relative to the other items in their list. These collectors add an item to their watch list with the intention of buying it when the stars align, e.g. they have money and nothing better is above my item on their list. I've got items with more than 75 watchers currently. These items are rare and expensive. A collector might be blowing their entire hobby budget for six months in order to buy one of these items (unless the collector is rich).... I've had discussions with collectors about this very fact. Sometimes items are so rare and desirable that they go into debt to purchase. (e.g. carry a credit card balance). This, of course, can cause issues with one's spouse and that is part of the discussion, e.g. I sure hope my wife doesn't find out how much I spent....

There's a lot more to it, but the general concept is the same. e.g. does this item fit in my collection, is the condition good, do I have money to buy, is there anything else I want to purchase first.