Shocks are easy for shops to replace and to make money on. They can replace them with no knowledge about your car and make money. Did they shake on the rear links looking for bad bushings. If they did not, find another shop.
I don't know why the right rear wears worse than the left rear, but I just know that it happens. I've maintained over a million miles worth of these cars, mostly 123's and 124's and I've seen it happen too many times. Keep plenty of air in the rear tires particularly.