Not sure if I confused you or you were just talking about subs in general rather than in response to my post.
Last year they had another landscaper trim their shrubs. This year they called me. I had no prior involvement with them. I decided that the work they wanted done and the price they were willing to pay was more suitable for my son, who worked with me for a couple of summers, so had some experience. So I just referred it to him. I didn't need him this summer, deciding instead to train his brother. Besides he could make more money working on his own than with me.
I do sub and sometimes refer work to a Master Gardener whom I've known for 20 years or so. She's good for the lighter labor and the tedious stuff I don't want to mess with....mostly flower beds.