If you don't trust the shop, why did you go there?
If the concern wasn't evident before the repair, it shouldn't be there after the repair..... much is going to hinge on what the RO that you signed stated as a concern....
At the same time, you guys in the states do have a hard time with charlatans.... Guys with a $99 Sears tool kit can open a shop and call themselves automotive techs with no knowledge, no experience and no scruples.
FWIW, I have seen a few vehicles where the finish on the rotors after machining has resulted in an un-nerving noise and feel.... possibly akin to the chatter you are feeling. These sorts of concerns I usually associate with poor shops...... especially since any brake repair deserves an extensive road test to both seat in the new friction surfaces and to ensure that nothing has been overlooked....