As a CRI you cannot teach a student without a licence. Only an FI can.
It's not about money. The whole idea is to get people who wouldn't otherwise think of paying for a quick flight, into the air and experience it for the first time. The free flight is an attraction and the volunteers are told specifically that it's not a lesson it's just an experience. It's not time which can be logged unless the pilot is an FI, which most are not.
I know for a fact it works. Up to you whether you want to do it.