I think guests are generally expected to buy something. Which is why I never go to those things.

I had a friend once casually trying to sell me a $100 necklace through one of those schemes. I was like: how much do you actually make on those 100 dollars? She said one fifth of the price. I was like wtf? So how about I give you $20. That way you get your money, I don't have to buy an expensive necklace I'll never wear, and you keep an extra necklace to sell to someone else? She was like "awesome" lol