Ok, using my ninja-like powers, I found this original thread. Try to find out from your invoice/statement/bill what they replaced.
Then TELL US.

So, from what I am reading, they replaced SOMETHING and now the car turns over but won't run.
SO, did it 'turn over but not run' before they touched it? Or did it not even turn over before they changed the module? WHICH IS IT?

We have GOT to have answers to these questions in order to help you. Be patient and informative - and keep in mind that SIMPLE CHEAP stuff can fail and keep the car from starting - and yet, not set a code. That is to say, if you are not experienced with the Crossfire or the SLK320, you will be lost - as in the case with your car and your shop.

If it is turning over and not starting, the Crank sensor, the battery and a lack of fuel flow/pressure (bad pump, bad fuel filter/regulator, bad solder or relay on the RCM that feeds the pump) would be the first things I'd check.

As to fuel issues, in the Roadsters (and I BET in the coupes as well), if you are QUIET and you turn the key to "ON" BUT DO NOT TURN THE KEY ALL THE WAY TO START - (This is after the car has sat overnight), you will hear the fuel pump run for about 3-4 seconds. If you do not hear the hum of the pump OR if you hear it and it never stops humming - I think you are about to find your issue! If you don't hear the pump, the RCM relay or solder is probably the issue. If you hear it and it won't stop humming, then the pump is bad, the regulator is bad - OR the car is out of gas!