Watch out for a tour guide who takes you to a duty-free shop where they pressure you to buy high-priced health supplements or the like. This is a scam. On a tour bus, the guide gets people excited about a product and then takes everyone to a duty-free shop run by someone who is not Japanese, where they get you to buy a large amount of a health food or such product. Such incidents are known. On the tour, they will take you to a place outside a city and say things like, "All Japanese people use this," or "It won't work if you buy any less than one year's worth." Even if the guide or the shop staff pushes you to buy something, always check first on the internet what that product is, its price, and other information. Shops can set whatever price they want for a product, so don't believe it if they say, "They sell this at the same price everywhere in Japan."
By law, people are not allowed to call things in the category of health foods "medicine." They can't say things like "It will fix this in your body" or otherwise talk about what it can help with. Or, if you buy a product because the person selling it to you gives you that kind of explanation, you are allowed to return the product to the shop and get your money back. So be sure to remember who told you what, as proof.