Generally I refer those I’ve worked with in the past who did great work, finished the job on time at or below quoted price and who were respectful of requests by myself or client (I.e. making certain gates were closed so dogs didn’t get out, not playing loud music, not disturbing the neighbors, doing a thorough cleanup afterwards, etc.).  I’ve also used others who were highly recommended by agents in our brokerage when my “go-to folks” were not available.