Have you ever read FAR 43-D?
(a) Each person performing an annual or 100-hour inspection shall, before that inspection, remove or open all necessary inspection plates, access doors, fairing, and cowling. He shall thoroughly clean the aircraft and aircraft engine.
Where does it say have his friends do--?
And 43.15
My signature and licence number in a logbook means I have performed and/or personally supervised the work to the extent necessary to ensure airworthiness.