What should be the response if"Often, celebrities' contract to endorse a product, but should they use the product regularly, or even like the product before they are allowed to claim that they "endorse" the product?"

What should be the response, If you were assigned to sell a product called "Sweet Treats" with the slogan, "so sweet, it will make you tweet," but you thought the product tasted sour, and not at all sweet, what would you do?

Where the line is between harmlessly implying that someone is promoting a product, and someone dishonestly claiming that they genuinely believe the product is the best?