Charging by induction seems very unintuitive to me. Let me explain:
Consider a positively charged rod and a neutrally charged conductor. You can charge it by induction by earthing it and not lose charge on the rod. You can then use this potential difference in the spherical conductor as energy. This can be repeated many times. Does this not violate the law of conservation of energy?
Also, why does charging by friction work? Consider conductors $A$ and $B$, which I charge by rubbing together. Assume that $A$ gains electrons during the charging process and $B$ loses them. But, as soon as $A$ gains an electron, that electron should move back to $B$, since we have a potential difference and a path for conduction.