I'm in Blackwater and I need charm to fix the tavern owner so I can finish the main quest. I have horrible stats in magical fields though, but I really don't want to restart.
I have amazing stats in all magic fields and I still can't charm anyone .. mostly because I'm not sure there is any such spell. Just don't annoy them in the first place!
There is such a spell, it's of medium difficulty, I don't remember exactly how much wisdom and divination you need for it, but there is a cloak that helps with both as well as a ring for wisdom, so you should be able to find enough items to learn it.
I just found it randomly spawned in the inventory of the Magic vendor in Blackwater, it's definitely not something he normally carries. I'm not entirely sure if it could help you talk the inn keeper down, I tested it out and it does not appear to let me talk to an NPC who has been charmed. Additionally level 3 Charm was insufficient to actually charmthe Inn Keeper but a message did suggest that a higher level Charm may have worked.