I know you will pay taxi correctly however, do you have any idea whether you have paid the driver properly ?
Okay actually this is very important when you travel overseas whereby you are not very familiar with local note, please ensure that you have the right note with correct amount before you hand it to anybody ( cashier, seller, taxi driver etc ), and most importantly while you hand it please get the acknowledgment from them the amount you give and if any change they must return to you. Why so troublesome ? This is all for your own safety, this is really painful when you think you got it right then suddenly they still ask you for more yet you have no proof to defend since you simply hand it without acknowledgment.
So again please check and have the acknowledgment, it is very important. Then why the taxi driver ? Please do not get me wrong ! There are millions of righteous taxi driver out there, but also there are few who purposely cheat with such a method . They will take advantage most when you rush, as your are so nervous then you lower your alertness. For instance you have handed 50 dollar then suddenly they call you again and inform that you just give 10 dollar by showing the 10 dollar bill, so in this case what can you do ? no proof, no witness ! Exactly they trick you.
Always be vigilant, try to control yourself, never rush and again I have to emphasize " check the amount and get the acknowledgment from them" do not let your self be their prey.
Safety is always first priority while you enjoy travelling.