The buffet line is a simplified test, meant to isolate an effect. Compare going to the grocery store with making a grocery delivery shopping list. You will find that end caps, promotions, coupons, shelf position, etc. all have an effect on you.

You will also find a lot of literature saying these things don't work. What they mean is "they don't work in the way they were sold to the people buying the end cap." But they sure do have an effect.