Something I've not heard anyone else mention . . .
When your strolling through the Exhibit Area and you say to yourself . . . Hey Self! I'd like to learn more about that product, participate in that drawing, collect that swag, register for that give away, or the like. A nice person will inevitably come up to you and ask if they can scan your badge; with the sincere and heartfelt promise that they or their company will not spam you.
Well, sorry for the bad news, they will, so don't be surprised. I guess everything has its price (No Pun Intended)!