"I know a Guy" Home Brew Ruleset

At any point in the game, a player may enact the rule "I know a guy", that may have information, or help the group out of jam. The player then sketches a two to three sentence description of said NPC and hands them over to the GM -- broad stroke information such as name, occupation, how the character knows them.
The adventurers then go meet the NPC. Depending on the last interaction the character had with the NPC determines whether the player gets advantage or disadvantage during the meeting.
So as not to exploit this feature, a player may only use this once per session, and cannot use it more than two sessions in a row to allow for other players to use this ability. This feature does not automatically succeed for the interaction itself, and it cannot be "i know the dude that secretly has the mcguffin we need to complete the quest".
This is not just for city games, and it's not just for bards or other charisma heavy characters. The idea is to use the old Han Solo 'i know a guy' line to add depth to the campaign and add some NPC's with connections to the players and the world.