My friends and I are new to RP and we've only had one session of dnd-5e trying out the starter set. As we are quite into fantasy in general, we thought we could make our own PCs. So instead of playing the premade characters, they all created their own, complete with traits, quirks and rich background stories.
One of the players has created a rogue with an exciting and very rich background, in which the rogue is a smuggler on board a ship, owned and tied in with a larger smuggling ring of sorts. Plenty of room for me as the DM to explore and include in the setting later on. Obviously, such a person has a large network, and knows a guy in every large town or city.
In Phandalin (as described in the starter set campaign) there are quite a few NPCs. When the group of PCs stands outside Lionshield Coster managed by Linene Graywind, the player with the rogue PC convinces his party that he should do the bartering, and claims outright "I know that woman through my smuggling ring". He did, at first, haggle on behalf of the group - they had some loot they wanted to sell - but he had an ulterior motive: He asked Linene (the NPC) when he would receive some diamond from their mutual smuggler superior. I went along with it and the PC and NPC had a quick conversation about it. It is not really an issue at this point, though some of the other players though it strange that he suddently could decide such things. It did, however, get me thinking:
Who should decide who knows who? What if players claim that their PCs are familiar or friends with an NPC that I, as the DM, planned to be a major antagonist to them? I know I could just let them know each other and create tension that way, but sometimes I figure it will difficult to justify such sudden friendships. The vampire who has been asleep for centuries.. "Hey, I know that guy!" How can I say "No, you don't know that NPC", without saying no directly?