I would be tempted to try some fairly aggressive clay over it before handing it over to a garage. (sorry if this has been suggested before - haven't read the whole thread.) It sounds like overspray or the like, easily removable with clay.
There aren't many garages that I would let near my car with a rotary polisher. Generally what you will find is that they attack the paint with the most aggressive polish that they have got and leave extensive marring and buffer trails on the areas they have been working on.
If clay doesn't work then I would contact a detailer in your area (check on detailing world) and get them to have a look at it and determine what your next move could be.
Sorry if this sounds disparaging against garages but I would think long and hard before leaving my car with a garage for any sort of polishing. Thankfully as I was a pro detailer until recently I don't have to!