Who's at the Door?

Saturday afternoon, Greg and I were sitting in the living room, enjoying the sunshine when the doorbell rang. At the door was a young woman, perhaps 20 years old, who introduced herself as a neighbour. She said that she was very embarrassed, couldn't believe her situation, but was desperate. You see, her mom was being discharged from the hospital and she had to go and pick her up, and take her home in taxi. She had already bargained a half price deal with the taxi company but the problem was that she had no money as she doesn't get paid until next Friday. Would it be at all possible if she could borrow the money and pay us back on payday? Being the kind man that he is, Greg managed to scrounge up $8 (from MY work bag!) and gave it to her. He even said not to worry about paying it back. She thanked him profusely, promised to pay it back, and then went on to ask the lady next door.
As I was contemplating whether I should drive her to the hospital myself (after all what are good neighbours for?) Greg called me back into the living room and said that he thought we'd just been scammed. What?!?! We live in a house with an excellent vantage point of both ends of a crescent thanks to our bay window. He pointed out a black car that was idling mid-street and said that he had seen the driver moments earlier walking around looking up various driveways. Now he wondered if the woman and driver were together. Just then the woman walked down our neighbour's drive and headed in the opposite direction as the car. At that moment, the car also made it's move and headed away. We wondered if they were going to meet at the bottom of the next street corner. Greg jumped in our car and slowly followed the woman. He was able to stay out of view and sure enough, just when she thought no one had seen her, she jumped into the car! I'm not sure what Greg was thinking because in this day and age when everyone seems to pack a gun, he made his Dukes of Hazzard move and pulled his car in front of theirs so they couldn't move forward! He got out of the car and confronted them. The woman was a very good liar. She said that her friend had just at that moment turned up to give her a ride, how lucky was that?! Greg called them bullshitters, said he had seen the whole thing, how the guy was waiting for her at the corner etc. He said that he knew that they were scamming the neighbourhood, that he had their description and their license plate number. Greg said that they looked very scared at having been caught, and for what it's worth, she did give him our money back. She had at least $40 worth of bills and change, so she'd probably been to quite a few of the neighbours doors.
When he got home, he did make a call to the police with the complaint, their plate number and description but who knows if they were pulled over. I'm sure the police have bigger and better things to worry about than a couple of scammers, but still, they are stealing and should be stopped.
We went over to our next door neighbour and explained what happened. She had given the woman the full $20, but as she handed the money over had said to her "I'm giving you this money in God's name." Bless her. She figured that the woman must have really needed the money, whatever the reason.
This experience has left me with a sour taste in my mouth. How can you trust anybody at the door anymore? When we first moved in, I was dreading having the Jehova's knocking at our door. They came and went and haven't bothered coming around again. But in any given week, there are people coming around canvassing for charity...how do you really know that the money is going to charity, and not directly into the canvassers pocket? I do donate money to a few charities of my choice, mainly homeless shelters, and I donate directly to the shelter. Honestly, after this scam, I don't think I'll be doling out any money at the door anymore. I am definitely not as trusting as I was a week ago.
Any thoughts on this?