Waxman,
I would think that selling at a discount or donating
tokens to a charity for their resale offers a number of advantages:
1.) Flexibility on the part of the charity to sell them over time, and not be restricted to a one day event.
2.) Avoids the uncertainty of a bad weather day, should you plan an event for a Saturday and it is a washout.
3.) Allows them complete upside on the amount of money they can make, based on how hard they work to sell the wash cards. A one day event might be limited to the actual capacity of the wash equipment in use.
4.) Allows the charity the ability to tailor their "profit" depending on the amount that they want to make per wash (up to face value). ie: I sell a local Church $10 wash cards for $5. They can sell them at full face value and make $5 or sell them at a discount and make a little less.
5.) The goodwill created by your association with the charity's fundraiser is spread out over many days, weeks, or months as the buyers of the cards come in to redeem their wash. If it all happens on one day, they might be out of town, working, or otherwise occupied and not aware of your public stewardship.
6.) Any single day event at your wash is probably going to be attended or actually "manned" by some of the charity workers, which raises all sorts of liability questions associated with the risk of these non-car wash oriented people working at your site.
7.) Like the "money multiplier" you read about in Economics 101, the charity workers and the card buyers are aware of your generosity, but if the buyers give the cards away as gifts, another layer of people are then made aware.
Single day events have their advantages too, which I think are mainly around the ability to have your staff on site interacting with the customers and charity workers and helping them to associate your business with being a good neighbor.
Just my thoughts.
ScottV