It's about CONTROL
A gives B 20 hours work a week to be done Mon, Wed, Fri @ 10 - 4
A agrees weekly payment
A supplies B tools & materials & set price per week
A is really controlling, so A is Employer
Same scenario:
A gives B work that could take 20 hours per week, B does it how and when he wants, maybe faster/slower
B submits monthly invoice to A
B supplies own tools & materials, may buy them from A on monthly payment arrangement
B now has more control, so B is self-employed