Clerk: Do you need help?

Carol: Yes, please. I'm looking for shampoo, but I cannot find it.

Clerk: It's at the end of this aisle.

Carol: Can you recommend me a brand?

Clerk: Yes, this one is good and only costs $1.50.

Carol: Do you have a cheaper one?

Clerk: Wait... This one cost $1.

Carol: I'll take it. Thanks.

Why does she ask for help?