Kevin MacLeod is great - I've used his music in a couple of work projects.
Originally Posted by Lucky Day 
As for a store, the premise of the game is the player is trapped in a dungeon so city market place don't make a lot of sense. Underground nomadic dwarfs caravans then? Maybe..maybe not.
I like the dwarf caravan idea. It could also be goblins, deep gnomes or other opportunistic underground races making some gold off of the "captive audience". I guess it all depends on if any kind of organized societies exist in the dungeon.
Some roguelikes just stick merchants in the middle of dungeons without any regard to realism, so you could go that route too.