The Knockers Guild is a fraternal order of dwarves, goblins, buccas, kobolds, gnomes and other earth elves who have banded together to help a fellow out, make a little extra gold, and have a little fun by the by. Any grubby, ugly little man who lives in a mine or dungeon, and has a little good in his heart, might join. The Knockers walk the halls of the deepest megadungeons, tapping on the floor as they go with the distinctive silver-blue knocker's lanterns they use to light the way for travelers. Meeting a knocker is generally a good thing, though it can be bewildering -- their logic isn't always logical by surface standards. Knockers have been known to mention trivial dangers like a handful of greedy goblins while ignoring very big things like a dragon -- which really is very obvious, so why would anyone need to mention it? They've been known to charge small sums for maps to very large treasures, or vice versa. Some will treat you like a long lost friend the first time they meet you. Others you've met before might walk right by without even an offer of assistance.
When you meet a knocker, he always has the silver-blue lantern that signals his membership in the guild. He will never part with it, and its light will go out forever if he dies or it is taken from him.
He also has one of the following things to share (Roll 1d6).
1. Local Map: The knocker has (or is willing to sketch up on the spot) a map of some of the local areas of the dungeon. He doesn't need it (he has a natural sense for which way to go underground, you see), but he's happy to part with it. If there are monsters in the rooms that he knows about, or other major features, he might mention those too.
2. Treasure Map: The knocker has or is willing to sketch up a map to the nearest treasure cache he knows about. He may also tell you about guardian monsters.
3. Naturalists Sketches of Wandering Monsters: Roll 1d6 times on your wandering monster tables. The knocker can tell you that these monsters are wandering about the halls. Feel free to liven up the gossip about each monster -- who or what do they like to eat, who do they hate in the dungeon, and who do they pal around with.
4. Cakes and Wine: He has good cakes and fine wine, enough to refresh 1d6 adventurers. Each adventurer who partakes in the cakes and wine will regain 1d6 hit points. Of course, you've also just accepted food from a fairy. Which may or may not mean something some day down the road.
5. Knocker Weed: The knocker carries good pipe weed to share. Taking a pull from the pipe grants the character infravision 60' for the next 2d6 turns.
6. The Key: The key opens any locked door in the dungeon. It must be rapped solidly against the door, at which point it makes a loud knocking sound and the door swings open. Each time the key is used, roll one die. On an odd roll, that was the last charge, and the key loses its ability to open future doors (don't tell the players until they try to use it again, at which point it vanishes loudly when used to knock). On an even roll, the key retains its charge. Any time the key is used, roll a wandering monster check due to the noise.
No goods or services are free, of course. That would be very bad luck. But the price of any given item will depend on your reaction check. On a positive reaction roll, goods and services cost a few copper pennies. On a negative reaction roll, it's gold and maybe even jewels -- the price will be higher the deeper your pockets are, and the deeper your need. On a very negative roll, the knocker might ask for something personal -- a treasured possession, a lock of hair, or even a debt. This may be harmless, and often is. But sometime in the future the knocker may come calling for a returned favor.
Needless to say, if you deal badly with the knockers, they will deal badly with you.