you are worried about soot in the exhaust - I think you should see some real cars then - every car in the world has a blacked out exhaust pipe because the engine consumes "hydrocarbon" fuel. It will shoot some soot. Its all normal.
Whatever spray was shot into the intake would have no affect on the injectors as they have their own fuel feed in which the mechanic would have never been able to spray it.
btw - there is no need to clean the throttle body - unless it actually is getting jammed while working. Infact some manufacturers warn of "excessive" cleaning which may damage the PTFE bushings on their throttle plate axle.
My Benz has approximately 175,000 miles on it (280,000 kms) and its throttle is working perfect, its nasty as a garbage bin but no problems in acceleration, idling etc. The throttle does open 100% in some driving conditions and has never reported any error - MB instruct that if a throttle motor feedback error pops up then proceed to clean its edges only and do not flood it.