I'm shopping for someone else...
Da standard "please bear with me --- I'm not familiar with this type or purchase" preamble-remark dat you ruefully tell a store-employee whom you ask for assistance in finding/choosing one or more items dat you never use yourself, and so you have less of an idea of how to shop for it or maybe even where it's stocked in da store.
Two good examples of when you might tell a staffperson, "I'm shopping for someone else..." might be if you were looking for a type of media-entertainment (such as books, music, or movies) dat you have no interest in yourself, or if you merely lived a simple bachelor's existence and were procuring "fussy female stuff" items for a lady-friend, such as cosmetics, dress-up clothing, fancy table-setting accessories, etc.