i have found that with events like this, trying to sell on the spot is a hard deal. People want to have the fun of taking the photo, but are very reluctant to shell out any cash. Just look at how popular photo booths are at wedding. They're always packed....why, because it's FREE.
If the guests had to pay to use it, it would be a ghost town venture.
Digital has caused this mentality. It's always better to work out some deal where you get paid up front from the hiring party and you provide each guest with a photo. But even getting that anymore is hard to do.
Cell phones, cheap digital pocket cameras has changed the entire mentality of people
willingly shelving out money for photos at event anymore.