At my store, if you don't offer the sales basket item, the customer gets it for free. When I used to help out up front, I had to ask a bald man if he wanted shampoo. He just looked at me, I smiled and said, "I know, but I don't feel like giving it away for free" (the signs explains what I meant by that). He just nodded and said he understood. Other times, when the same situation would arise, I would say, "Even though I already know the answer to this, I have to ask...". Customers will understand at that point.