How in the world would the thieving couple know that this woman had a valuable necklace around her neck? Did they simply start their ruse by asking directions and then escalate their scheme after seeing the necklace? Do they stake out parking lots and know which ones are likely to bear fruit?

I am a little older than the woman who was victimized by this nasty couple and if I was victimized as she was it would be a long time before I felt safe again. In Palo Alto. I sometimes think our city must have a reputation for being an easy mark.

This is Detective 101 at play, I think. I would ask the victim where she was before she went to the Walgreens store. Then see if there is any camera surveillance where she came from. The perpetrators likely saw her at her previous destination, and realized she would be a perfect mark. Their car was probably where she was, and one or both of the perpetrators may have followed her around to get a feel for how "easy" she might be.

Alternatively, they could have been cruising, looking for someone wearing visible jewelry, and in the age bracket they prefer to victimize.

The more articles that are published describing the perfect victim, the more crooks out there realize PA is full of easy marks. But we need to know to be alert to stuff like this. In this case someone may have noticed something before the swap occurred.

Unless they sell it on ebay, any place that buys used jewelry checks to see if the item has been stolen. Very easy to do, with internet resources.

Sometimes it doesn't pay to be nice. Years ago I was in NYC walking along and someone pulled over and asked me for directions. Not being from there, I said I couldn't help them. They cursed a blue streak and I thought they might get out of the car and beat me up! I walked into the nearest business. I could have looked like a clueless tourist and face robbery or worse. Now when I'm in a strange place and anybody asks me for directions, I pretend to be deaf. And if somebody on El Camino can't find 101, boy... wait till they find out about the fees to drive that "free" way.