There are two ways to look up guest history from Sales:

 

The difference between History and Summary is that Summary lists those cases where the guest is directly attached to the sale by selecting set or add guest. History includes the latter cases as well as cases where the guest purchased an item without being directly attached to the sale. If a guest purchases a candy bar, for example, and pays using an In-House Cards card, that guest is not directly attached to the sale, but the sale still shows up under the History button because the guest is associated via the In-House Cards item.