Elongated shopper

One who takes longer then necessary while shopping

Eryn is such an elongated shopper, it's hard for her go to the department store and grocery store in under 3 hours.

secret shopper

Refers to members of the less-affluent sector of mall-customers who merely wish to purchase regular groceries and/or household products in bulk, but who do not buy enough yearly volume to justify paying the exorbitant "membership fee" that the "big box" stores like Sam's Club charge. These limited-income folks therefore discreetly approach "enrolled" club-members who have either just arrived at the store or are currently pushing their carts around the aisles, and quietly ask them if they could please also purchase the merchandise that the indigent people want along with the items on their own shopping lists, and then afterwards they all meet back up outside in the parking lot where there are no prying eyes from the store's staff, and the grateful low-income families carefully go over the obliging club-members' store-receipts to total up the costs of the "additionally-purchased" items, and then reimburse the members for the appropriate amounts in cash.

Being a secret shopper can indeed be a great way to save on household-staple items; just watch out for Sam's Club chiselers, however.