How to panhandle a quarter

Once you spot your helpful citizen, go up to him with four quarters in your hand. "Can I exchange my quarters for a dollar?"

Make the transaction or switch. He/she gives you a dollar bill, and you give your four quarters to your new friend.

Then, you ask "Hey can you spare a quarter?"

You have already made contact, engaged the person, and you made a legit exchange, a honest transaction; you have established trust. And your new friend knows that you know he has four quarters, making it impossible to truthfully tell you that he doesn't have any change.