So, the colporteurs used to sell Brown's Wonder Salve along with the books.
It said the society paid $.17 for it and sold it to the colporteurs at $.25 ( I think. It was hard to read here.) Then, they sold it to householders along with the Bible literature.
Then, whenever the government got onto them for not paying taxes on these side ventures (like Miracle Wheat), Rutherford claimed that he wasn't making money on them. Everything was just sold at cost.
I remember using that line door to door in the '70s and '80s.
It's an interesting read if you can zoom in close enough.