I have been to several of these things and I tend to go with an open mind. If I find something I like, I will get it, but if not, then I have not compunction to buy.
I have also held a Pampered Chef party where upwards of 50 people showed (all said they showed up because they new I was cooking!!). I didn't care one whit if they bought anything, I was just throwing the party to have a ton of friend show up, eat, and have fun (unfortunately, there was still a TON of food left over.....well, it was good to take to work the next day!)
One of my former bosses would throw a massive party ever quarter or so. She loved the Longaberger baskets so she'd have a rep there as well as a Mary Kay rep and a couple of other ones, but she didn't care if anyone bought anything. Like me, she was just throwing the party to have friends over and to gather around the buffet (and wine counter!!!).
Now, my schedule is such that when I am invited, invariably it's on the weekend (I work weekend nights), so going isn't an issue!