warning lights/ diagnostic services

i was curious having read loads of your threads regarding getting diagnostic work done on your cars in main dealers alot of people seem to think they have been fleeced just because a light was on .and was wondering is it beacause they didnt actually see the work been done or because the cost of the diagnostic was too expensive where some tool just connected a computer to your car and says bla bla bla is wrong and charges you 100 quid and still hasnt fixed your car??

what would you be happy to pay for this service just as peace of mind so when you bring your car to get the work done you already have a good idea what is wrong with you car or you cando it your self?

the reason im asking this is it seems to be a big bone of contention for all you car owners and diy buffs who like playing with your own cars and maybe its time to do something about it ,would there be a market for it??

I recently left my car into a garage to have a diagnostic done on it. The guy told me he had used 2 different machines and still couldnt find what the fault was. I gave him €50 even though he said no charge. I was happy that he had tried his best and felt he deserved to be paid acordingly.

you can also buy your own reader to read the diagnostic codes....
or build it your self!!