Some Software Engineering research requires human evaluation. Unlike the program you have control, human factors are sometimes out of your control. To make sure evaluation goes well, the following should be done:
1. Have some backup evaluators in case someone could not complete on time. Even the evaluation is very important, some people may not take it seriously or forget it.
2. Make sure the quality of evaluators, not quantity. To ensure quality, preparing gift card is not a bad idea.