Lockpicking is exclusive for rogues, the other classes don't have access to it, ever.
Sell prices are always 50% of the item's original value.
For the fortune teller: She is also later available at the purchasable house in the Town of Beginnings (well, not the fortune teller exactly, just the Memory Lane location she takes you to).
For combat balance: Yep, I'll be honest, one of the issues I've had for a long while is lack of playtesting to see what works and what doesn't in combat. For the next update I've already completely revamped the blood magus moveset along with the order they're received, might do that for other classes as well.
Unfortunately the "math" to be done is rather complicated, since you have to factor in perks picked, armors found etc. etc. Until now it was way too often that the players found a way to "break" the game, so I've had to keep upping the difficulty with almost every patch. Frankly it makes me happy that people are finally unable to just breeze through everything. There is still a lot of work to be done on that end (for example I will probably turn all the buff moves into team buffs rather than self-buffs), but I need as much user data as I can gather for that (how they play I mean).