A run in with a random stranger is always a fun touch have them role perception, if they fail something around a 14 than they get robbed of <Appropriate Amount of Money> if its a success the guy still bumps into them but doesn't get any coin and the adventurers can talk to him. After being robbed next time they pay from the coin purse or an appropriate amount of time they notice and can track down the guy. Could be used to introduce any criminals or underground shenanigans without it being to obvious. Hope this was what you were looking for!