There are no laws I'm aware of that prevent anyone from working on guns. There is no "licensing" to be a gunsmith. Its why its hard to find a good one since any yahoo with a screwdriver can call themselves a gunsmith.
You do not need a ffl to work on guns while the customer waits. If it is left in your possession and the customer leaves you need an ffl.
Every state I know of says that if your engaged in working for pay you either need to be an employee of a business have a business license or work for less than a certain amount per year which varies state to state.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
"I crapped my pants to avoid the draft!!" -Ted Nugent