that's a very big step up for the scammers, to set up an actual roadblock

If you are sure they are scammers why don't you call police then?

Actually this isnt new, it has been happening at least for the last couple of years occasionally, i remember it occurring two or three times around Meyrin in 2012/13.  They do it near the borders normally with high visibility jackets to actually make you think they are border police or certainly people of some authority. Their activity creates its own queue of cars so actually looks exactly as the real thing would. Its very clever, who wouldnt stop for someone who looks like a border patrol?

They were in Divonne border last week.

Between CERN and Thoiry it happenned to me twice that a car stood in the middle of nowhere on the side of the "highway". 

A guy outside the car said he needed petrol while his wife waited w a baby inside. He offered is wedding ring if I gave him money. And to pay it back later.

It's not really new, they are at the Divonne border quite often for at least a year or two. I told the french custom officers several times, but it's like they don't really care.

I've seen this once in a mall car park in Villeneuve. I slowed down thinking they were either local cops or workers...then I saw their faces, and I locked the car doors and speed up. 

Yes, ROMANIAN GIPSYS! They set up their camps and start performing their daily routines.

There's one now beside Leclerc behind the airport. I bet you they were coming from there.

They also stop in the middle of the motorways to sell "gold" or "carpets" or ask you for "help "while their cousins empty your boot . Looks like there's a law for them and another one for regular taypayers. 

Don't bother to ring the cops, too busy harrassing hookers in Pacquis.

I hear there's a band of Spanish operating in the region trying to sell fake jamon. I bet you're one of them.

;)  keep quiet and I'll give you half of the benefits! 

I'm in for 50 francs worth of counterfit jamon!

Deal!