What would someone who can give people powers want in the long run?

well, he could be good or bad...if he were a good guy, then maybe simply making them swear to use their powers only for good and not for selfish or wicked reasons, and if they break the contract they not only lose their power but they receive the opposite disability (if they were super strong, and they used that power for evil, they would then become like partially paralyzed, if they can fly they become really fat so they can't even jump, if they were invisible they become really brightly colored so everyone's attention is drawn to them)...if the guy with the contracts is evil, then maybe he is like Rumpelstiltskin and the signer has to give him their first born child, and if they don't have children by a certain age they become his slaves...he then gives the children powers and forces them to be his slaves and join his evil army (or makes the superheroes join his army if they don't have children)...this would of course eventually lead to an epic battle between hero parents and evil children...just a thought...

He can get entertainment out of it.If you have watched durarara, you would know about Izaya Orihara.He likes to annoy people and play with their lives for the absolute reason of having some entertainment out of human emotions and behaviour.He doesn't deliver people power though, he's that "info broker" so he gives people information and leads them towards bad situations.You can kind of get ideas from him.