It's called Backshish (or Baksheesh): a gratuity, a tip or bribe paid to expedite service. The tourist is a vulnerable victim to this practice that is everywhere. Mark Twain wrote about it, "—and out of their infidel throats, with one accord, burst an agonizing and most infernal chorus: 'Howajji, bucksheesh! howajji, bucksheesh! howajji, bucksheesh! bucksheesh! bucksheesh!' I never was in a storm like that before."