If you’re buying three products, then it indicates you believe in those products. When you say it’s not a viable business, but you’re buying the product, your actions say you think the products are worthwhile, which sends a message to him that there’s a chance.
His upline can also say, “They can’t think it’s too bad if they’re buying the products.”
I’d also take the labels, spend some time on Google, and compare their products to what you find in the stores. If you can produce competing products with almost the same or similar ingredients for less, then you’ll be making a point.
As long as you’re giving him some income, he can hope for more and it delays the time when he’s broke and has nothing to spend on it.