Guys,
I own a workshop in Canberra and can see where you are coming from
To give you an idea what happens with my shop, I normally charge $100/hr labour, in that you get my knowledge that i have learnt over the years of working on import cars, but in saying that if someone comes in asking for advise i am happy to give that, but when people try and tell me how to do something essentially meaning that the job is done by them just using my hand i either turn them around and send them packing or can and have charged them more.
In saying that I am not going to side with either the workshop in question or the customer as it is not beneficial for myself or you.
There can be any reason for them to charge that but it is always up to you to accept that and if you think that's unacceptable then you can refuse it.
If some one refused my quotes i don't take offence to that to me that means they would not want to use my hands and knowledge or experience.
Having peace of mind with work being carried out by a mechanic will always favor the consumer especially with fair trading. If you dont think the work is up to standard either talking to them about it or taking it to Fair Trading will fix that issue.
But overall mechanics do make mistakes or have fked up here and there but for those that what to do the work themselves sure thing good luck on your ventures i hope it all goes well.