A friend's dd is in university and has become a demonstrator for a very expensive product. I can't afford it, even if I wanted to buy it. I've been invited to a demo party and my DM says you can't go to these things without buying something as the host doesn't make anything. She proceeded to tell me how many things she bought from Pippa Dee/Tupperware/PartyLite just to "support the host". DM is prone to strange ideas, but I just want to check if this is a thing? Is it better for me not to go if I know I won't purchase anything?