About venue "rules", and when to follow them.

Okay. Talking almost specifically about Fall Massive here, but I'm trying to take that experience and apply it to posterity.

So the FAQ for the event explicitly stated that absolutely NO backpacks were allowed, and no purses over 10 x 10 x 6 inches. So I go there with a wristlet chained to my pants and my cigarettes/phone/lighter shoved into my pockets, only to see literally hundreds of people walking around with backpacks. Considering my previous mini-rant about my alligator backpack, I was understandably pissed that I spent the night worrying about how best to store my items, whereas these rule-flouters were skipping around with their backpacks without a care in the world!

I know, I'm dramatic. Anyway, the point/tl;dr is:

Is there a way to know whether or not a rule like this will actually be enforced at future events?