Well, no.
But that's the point. The rest of the details are too much for the average consumer to gauge.
He could.
1) Use a wrong part or a used part that will wear out months down the line.
2) Damage other parts, or reassemble improperly causing parts to break moths down the line.
3) Over charge by a massive amount.
4) Rack up the bill by replacing things that don't need it.
5) And so on..
I could leave the shop with my car running and any or all of the above things could be true. And I'd say that if they are, than it isn't a good job.
As an example, the flexible part of my exhaust recently ripped clean, making my car sound like a T-Rex and endangering my life from carbon monoxide poisoning. This happened because either a mechanic I went to, or one the previous owner did forgot to replace a bracket that kept pressure off that part. It took at least a year for the shoddy work to result in the broken part, so I have no way of knowing (meaning, the market has no way of weeding out the incompetent mechanic).
Just like many manufacturers could have poisonous products, and without government oversight, no one makes the connection. The market can only perfect those things that are obvious to consumers. For things that make you sick, cost you money, or kill you farther down the line, the consumer's imperfect knowledge means that companies can do a terrible job and remain successful, as long as that terrible job isn't immediately apparent.
