Poor Misfortunate Souls: Shenanigans with the PF Witch

[Angry Bob]

The title alludes to my character's favorite hex, misfortune(plus cackle).

I'm considering doing something in my downtime that's not item creation. Namely, offering shady deals involving spellcasting to locals without the knowledge of the rest of my party. I've yet to run it by my DM, but the game is already atrociously broken, and adding to the story would only be received well by him. I'm mainly brainstorming right now.

What would you want out of these deals as a player? How would you want them to work? How would you run these as a DM? What limits would you impose? Would you add new rules or just allow alternative forms of payment, such as, say, one's voice, or something similarly exotic? What other things fit with this theme of payment?

What spells seem useful or necessary for this sort of thing?

tl;dr: My Witch wants to become a small-time(and eventually big-time) Mephistopheles figure. Tell me every thought you have ever had on the subject.

[Anathemata]

I'll have to get back to you on the spells, but your idea is GREAT.

This is the kind of things that give DMs a chance to expand their world and players unexpected opportunities to become more involved with that world. And, if you're doing it behind the party's back, that could invite many unforeseen consequences to add to the drama.

I would say to the player, make deals with merchants and eventually with merchant houses. These guys are hungry for any advantage, can provide you with (rather conspicuous) wealth, and give the DM a chance to involve you in wider-scale intrigues. After all, merchants go hand-in-hand with nobles, and are often the first to hear about mysterious whatnot going on in the wider world. Accept whatever weird compensation, but 'minor favors to be redeemed later' might be cool, or just unusual magic items. I like the idea of a stolen voice, or a lock of their firstborn's hair. Creepy.

As for DMs, I would advise to let you run pretty wild. But I wouldn't bail you out of trouble. If a temple or mafia organization decided to start hunting you and cared nothing for your 'mystique', that's on you. Part of being Mephistopheles is, well, consequences if you suck at it.