Guinea pigs will very very rarely bite. I've rescued guinea pigs for 5 years and have handled over 500 of them and I've only been bitten once and it was when I stuck my hand in the middle of a fight.
They have occasionally nibbled me, but as a general rule they don't tend to bite in defense like a hamster or a rat.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry