I see that Jim Bardwell is doing a presentation at MF that will explain how to understand personality styles using a system commonly called "DISC".
If you want to know why the best cleaner you know won't sell add ons....go to this program
If you want to know why the cleaner who adds on the most work seems to miss spots...go to this program
If you want ways to understand why some customers seem to "get you" and others can't stand you..and visa versa...go to this program.
If you want to know why Marty gets annoyed at Mark Saiger's videos ...go to this program
I could go on and on ....just go.
I use this system in my work and even interpersonal relationships nearly every day.