It's wrong to deceive a customer.
Jack is a salesperson and there are large incentives given for selling customers add-ons with products.
Jack wants to earn a large bonus to purchase a gift.
Jack provides a great reason explaining the value of the add-ons to the customer up front.
Jack opts the customer into buying add-ons and the customer signs without realizing it.
The customer actually wants the add-on and Jack gets a bonus.
The customer later notices this and complains to the store about Jack.