I traveled lots when I was young and learnt this the hard way. We kept having to give the Mexican police by Cabos San Lucas more and more USD everytime we went to get groceries.
Don't give money to ANYONE not even just a child, the police can be just as big of an issue.
At the point the wanted $50 we told them to fuck right off, but they just laughed at us and walked away knowing we would likely pay tomorrow.