There are a couple of good resources for preparing to improv. I recommend putting this in a blender, making a digestible soup out of it - pour it in a bath and absorb it through osmosis.
One of my favourite parts of this, is Robin D. Law's essay: Improvising Dialogue Sequences. Summary: Every meaningful interaction with an NPC has both a Petitioner (someone wishing to get something) and a Granter (someone who has the power to fulfil those wishes)
In order to satisfy the criteria a Granter imposes, the Petitioner needs to use leverage. Robin list several useful methods - I figure that each NPC will have a preferred method of leverage, that will unlock their ability to grant the petitioners wish. We can go further than that, why not give each NPC a secondary preferred method of leverage - using this will unlock their ability to grant wishes, but with a cost or at a reduced efficiency. Also they should have a method of leverage that will make unlocking their wish fulfilling potential harder - or - impossible.
Here's a rough example:
Appeals to Duty
So now we have a quick guide how to run this guy when he meets the players, these rules work if the burgomeister is both Petitioner or Granter. You could create two lists for each, but for my purposes this is simple enough. Furthermore i've put together a nice randomiser, so should I need motivations on the fly I can get them. *If you get multiples (you-will) re-roll*