My boys hadn't been handled much when I got them from the german version of craigslist (their previous owners bought what they THOUGHT was a pair of girls, then were overrun with gerbils and didn't have enough time to socialize them all). They were a bit bitey and timid anytime I put my hand in their habitat.

Well, due to a fight in the trio (one gerbil now lives alone with my mother after bloody fights with multiple gerbils, sometimes they really do need to live alone, which is very rare, gerbils really do need friends if possible, but that's another topic), they had to get over that pretty quickly as they needed twice daily wound cleanings and antibiotics.

My trick was that every time they would give me a nibble, I let them do their thing (no jerking away, no sudden movements that would startle them and make them fear me more), and I would just gently push their nose away with my finger which would release their bite (the hell raiser is still not tame, but is friendly, he's...special in his little gerbil brain).

The biting stopped within a couple days when they realized no harm was being done to them, and the biting didn't get the reaction they expected. They are completely tame now, I honestly didn't know gerbils could get this tame before I had to basically force them for their own good.