Workshops wouldn't be paying $7,000 and up for an injector cleaner if a $10 bottle of chemicals is going to do the same job.
Secondly, an injector clean is going to fix the long term build up of muck and grime on the injector nozzles, the vast majority of the time nobody would notice it happen as it quite some time for it to happen. Once a clean set of injectors have been fitted, it is then that you will notice how dirty they may have been.