What should I tell other people about giving money to a Beggar?
The Buddha has mentioned that it is the givers qualities that matters most in giving. He says for example that if he were to receive something from Ven. Sariputta, that would not be as meritorious as if he gave the same thing to Ven. Sariputta. 

So, if you are a person with Arya qualities, as long as your giving is also Arya, the effects will be much greater than that dictated by the receivers qualities. 

Arya giving is letting go at a distance.