i think that any workshop that is going to do discount dyno runs is probably going to give discount quality results. so in other words it will be a case of drive the car on, strap it down, quickly put the settings in, do the run, drive the car off and take money. so they probably wouldn't take as much time to get the settings on the dyno right (such as putting the intake temp sensor in the engine bay), etc. so readings wouldn't be quite as accurate as a full paid run.