Well you can't expect to scare everyone, but you can certainly try.
One thing I've found effective for myself is doing the unorthodox. Something they're not expecting. When you enter a haunted house for the first time, what do you expect the actors inside to do? People usually think the actors are going to simply snarl, yell, and keep their distance. But I don't want people to see what they expect. I want someone to think, "Uh, is suppose to be doing that? Should we get a doctor or something? Wait, wait, that's a little close. A little too close. Back off, weirdo!" What I do exactly are noises such as short rapid breathing (while trying to act like I'm chocking on my own tounge) and gargling. To make my body match the sound, I fake violent convulsions. To top it off, I get really close to the customers. How close? Close enough to literally count the hairs on their upper lip. One of the golden rules of the Haunted House is no touching. Which means we can get as up-close as we wish as long as we don't make contact. But you don't have to replicate all that to achieve your goal. Just remember "do the unexpected" (and hope for the best). If all goes well, it'll put a damper on the customers' sense of saftey and control.