Service Fees for Charity Events

Having a charity event to raise money for a rail-related cause? Trying to figure out how to annoy potential customers? Just setup your ticketing so would-be ticket buyers pay a 20% service fee when buying tickets to your event! I’m trying to find a way to buy tickets for the ORHF’s Santa Train without getting bent over… right now it looks like my only option is to drive over to southeast Portland to OMSI to buy the tickets in person (which really isn’t an option).