Officials frequently round up travellers and demand for documentation or to check their luggage.
If one writes down less than what one actually has, the excess may be confiscated. On both occasions, I was insistent that I was correct and after a while, the officials gave up. I am convinced that a firm response in public is always necessary if one does not want to subsidise these corrupt officials. You should bargain and ask for details of all possible costs. Clarify on matters to prepare for on any trekking trips.