The tour guide said the health food product was good for the body and that it would heal illness, so I bought it, but now I want to return it.

It is against the law to sell a health food product by claiming that it has medicinal effects or that it has the power to cure a certain physical ailment. If the store had an agreement that the guide would explain the product, and if you bought the product based on that explanation, you are entitled to return it and get a refund. However, it must be true that the store had an agreement with the guide to explain the product, and you need to have a record of some kind of what the guide said to persuade you to make the purchase.