Piggies don't have a vomit reflex, so youngsters need to discover the world by nibbling and licking and taking their cues from older more experienced piggies to learn what is safe and what not. Most piggies will grow out of it once they know their world.
Occasionally, a dominant piggy is trying it on with you by tweaking quite hard when he is settled, but you can discourage that gently, but firmly. Some piggies tweak fingers or clothing to signal that they want to go back home. Some traumatised piggies may also bite; avoid picking them up with your bare hands (use a cuddle cosy for that purpose). They will stop as soon as they settle in and no longer feel threatened.
Accidental bites can happen when your fingers are mistaken for a piece of veg that they smell of by an enthusiastic piggy (or very occasionally because of some scent they do NOT like).
Real, bad bites only happen if you either try to break up a serious fight with bare hands (always use a towel) or if for some reason a piggy is suddenly really frightened (by a sudden, sharp noise close by, for instance) and may hack into you by reflex.
But to reassure you: I have had piggies for well over twenty years in my life, but been bitten hard only about three times; twice accidentally and once through my own fault. Once in a decade is not too bad, is it?