Ask HN: Dealing with offers to work for your startup *part-time

I run an online education platform and have received offers from a number of people to help promote our business and work on the platform in various capacities. These tend to be for working part-time and often offering to work for free. As a bootstrapped startup, what approaches have you taken or seen to deciding who to work with, how to manage them and how to structure compensation/lack thereof? Thanks!