CHARGE A RETAINER FEE
Be sure to cover your costs by arranging an up-front payment, independent of image sales
When shooting weddings or other similar events, you can be fairly confident of the proportion of guests that will purchase prints from you. At school events, when the exact format and attendee engagement can be undecided and unpredictable, you need to reduce the impact of poor sales, not least because your images will have limited long-term significance. Consider charging a retainer fee, that is enough to cover your travel expenses to the venue and time preparing previews later. This can be contributed in small amounts by each attendee, who can be discounted this amount on their print order, for example.