My default understanding of bus conductors in SL is that a very few have manners or “pleasantness”. And almost none having both.
I know in some bus routes the correct balance is returned only if he is in a good mood enough to not to be greedy. 120 route from pettah to kesbewa is not such a bus route (thank you god) but a conductors never miss an opportunity give less balance when he can justify it. In most such cases we have to remember when we are getting off the bus to ask the conductor to give the remaining balance.
On one such rare situation last week (28.05.2011) when I had forgotten to do so, this conductor came from the other end of the bus to the rear end & handed over the balance. It was a day to remember.