staying in Phnom Penh for a while I can tell you that tipping is not expected. If you pay for a good meal in a restaurant you can tip $1-2 . But if you have paid $20 for a guide or driver they will not expect a tip. I understand that Americans like to tip wherever they go, as a European traveller I try to follow the local customs. And a poster here said that the average salary is $400 . That is just not true. The staff at the restaurants earn about $50 plus tip . Instead of tipping your guides or drivers (they are among the richer cambodians) you should give a few dollars to the streetkids. They really need it, or you can buy them food. $1 will buy a lot of food here.