Why favor ?

Why those not so familiar friend will call and ask favor ? Especially ask you to offer your personal connection to celebrity in town for their own benefit ?

I don't have an answer but gradually I devlop a pattern to deal with such an situation : 

1. Standard reply : I am not so familiar with them but won't mind to ask for them 

2. It's a no guarenrtee conversation 

3. If the friend is a long shot - I won't bother to even send the message - this will only show how native I am 

4. If any follow up request : my standard answer is : he / she won't be available then .

 Is there anything wrong on my side ? I will spend time to talk with the person who send their request but will not build the bridge and ruining my relationship.