Rescuing someone in a dungeon may lead to them offering you a reward. It may lead to players having a local contact for information and interactions in the future. But what if the person rescued was so talented the reward they offered was like a magic item?
The Royal Jeweler - I can make a brass automaton that mimics the movement of a real creature so truly it can pass as that creature! Come to me in the future and I will make one for you. Whatever creature you wish as long as it is no bigger than a small dog.
The Wise Woman - Take me to some dread place you will enter and I will ask my ancestors about it. Then I will give you a walnut that will roll toward treasure, an acorn that will roll toward lost friends, and a maple samara that will flutter back to the exit.
The Mad Hermit - I have gathered foul herbs enough to slather three of you so you will appear dead to the dead and beast to the beasts and foul impertinent to gentlefolk and scholars.
That's the idea anyway. I want it to be a kind of one time service, not something the players would go back to again and again. So it needs to be unique and powerful enough that the NPC can only afford it once. But also want it to function as another tool in the Player's adventuring toolbox. Something they will keep in mind for future heists or schemes. So it can't be a straight up reward, like if the wise woman gave the three seed to them and they would work in the next dungeon with no further help from her.