What to do for letters of reference if you want to apply to grad school but you've been self employed? Similar to this question How to secure recommendations and apply for PhD after having worked outside of academia for two years? but more specifically if you've been out of school and self-employed for a while, what options do you have for letters of reference? And AFAIK you need two letters, so if answers could provide multiple potential options that would be ideal :)
The source of the letters matters less than what they can convincingly say about your chances of success in the program you are applying to.
So choose referees who can write such letters. They might be clients, or managers, or former professors, or people you consulted professionally while self employed. People who know your work and your work ethic.