Yes, Mr. Schmoe can go break into any Benz. He and his forefathers have always done it. I doubt he will use the method I described. It is a typical amateur approach. The association he gets spreading his feet and placing his hands at the top of a car is demoralizing for him.
He will of course use a sofisticated method, and the passing crowd will take him for an owner getting into his car. Once inside, it will sometimes take a while before a driver is ready for take-off. Nothing suspicious about that.
One of the good things about the W124 is that it's not too hard to open. And not too hard to steal. Modern immobilizers have immobilized a lot more owners than thiefs. Companies like BMW and Audi has tried to lock the buggers out with complicated solutions, only to find that Mr. Schmoe could circumvent them with as silly things as that tennis ball trick. They have caught more owners than boogie-men.
Did any of you hear about the Thai minister that was prisoner for five hours in his government BNW because his battery zonked out and nobody could open the doors? Or something computerish like that.
Even the newest and most expensive MB's can be opened in the way I described, except the armoured ones. I think that is the result of correct thinking. What is worse? Losing a camera, or a window and a camera? I could go on and on about owners tangled in the anti theft web on modern cars, but the W124 and MB in general is not much represented.
When we tow in W124's that have been stolen, they will most often be what we call "key driven". The ignition lock is a weak point. It gets worn over time, and the risk for key jamming or theft is high. A worn lock is very easy to pick, and should be swapped with a new factory one or by an auto lock-smith. Installing an alarm will make the chance of normal theft minimal.