In most cases, the person who let you in is outside the auditorium and the booth is inside, so that person has no idea whether you bought anything or not (and probably doesn't care, anyway -- they are letting you in because they potentially want to make a sale, not because it's guaranteed. Also, that person has another job and frankly isn't likely to be paying attention to what you are doing even if you are in eyesight).
If you're really self-conscious about it, bring a backpack or something so that you could potentially have your bought merchandise in there when you are actually leaving empty-handed.
Similarly, the merchandise person has no idea whether you are a ticketholder or not, so they aren't going to rush you any more than they would rush anyone. Even if they did, I don't know why they would treat you any differently than anyone else.
"What was the name of that cheese that I like?"
"you can't run away forever...but there's nothing wrong with getting a good head start"
"well I hope and I pray, that maybe someday, you'll walk in the room with my heart"