In my business travel, I had been to a few cities and towns across Indoneisa. Custom's greed and abuse are all in a day work. One of the
things (of course the foolproof one is just pay) that had worked for me when they get too unreasonable was to raise the voice so it is audible to all around you, not forgetting to mention the name of the guy who is giving trouble. Caution: use with discretion.