Larian Studios Forums Divinity: Original Sin 2 Divinity - Original Sin 2 - General Lucky Charm and Thieving are gamebreaking.

Thieving gets exponentially better as you put more points into it, and each character can pickpocket once.
That means if you have some gear to get +4 thieving, you can pickpocket 6 times to clear any skill book merchant. If those characters also have some points in Thieving, then it gets even better.

I've looked pretty hard though, and +Thieving gear is pretty rare.