Other things to look out for, people at the airport try very hard to take your bags etc to the taxi, this ofcourse incurs a tip. Just got to keep saying no, even try their luck by carrying your bags WITH you without your permission and then still ask for a tip...
They also are quite good at giving you a personal tour of parts of the temples which also incur a tip at the end, you aren't told of this prior. Basicly anyone that comes to you are wanting something so I suggest keep your witts about you, we also had an attempted pick pocket by what looked like a 4 year old. Aparently the local gang groups use kids to help get extra funds for them.
All that said though, they are really nice people the legit ones. Got to think of how hard they have it and put it into perspective before pre-judging
Agreed! As @GarathG says, Just say No and be firm.. But i do agree they will try anything for a tip.