But, that idea ignores a fundamental problem with expert-based markets; it's impossible to me, as a non-consumer, to make a rational decision about which mechanic to use because to me, the mechanic is a black box. I don't have any way to immediately fact-check what they're telling me, and in the worst case, if a mechanic does something wrong, I may not find out about it until it's far to late to hold the do-er accountable. Thus, I can change mechanics based on the limited information I have available (price signals, perceived reputation) but, A) this distorts the market to optimize for low prices and perceived reputations instead of efficient prices for quality work, and B) I don't ultimately have any way of knowing whether I'm making the right decision when participating in this market. At least, not in the time frame where that knowledge is useful.
The same, holds true with 'free' health markets; I'm not a doctor so I can't accurately tell if my doctor is lying to me, which should cause similar distortions in an ostensibly free healthcare market. Additionally, as with an auto mechanic, if I need something done -now-, my demand for that service becomes completely inelastic, which means prices for emergency services/procedures should become obscenely high.
They already are today, and people are -already- getting forced into bankruptcy by emergency medical expenses, so I can't speak to whether or how a market sans insurance might change that phenomenon, but it seems to me that the goal ought to be to eliminate it entirely, and that in turn a 'free' healthcare market cannot be the end goal.
That said, I don't think I know enough about the subject to pick out a particular optimal solution to this problem. I like the -idea- of single payer or other universal healthcare solutions, but I haven't studied any of them in enough depth to analyse them critically; dealing with healthcare in the UK was a joy while I lived there, so I wouldn't mind having that experience here in the US, but that in turn requires a lot of government funding (among other things), and we can already see that that's unsustainable in the short term by what's happening to the ACA.
Yes it does because the mechanic is required to call you and say, "Upon further examination we also need to do ______ with will cost $XYZ. Do you want to proceed with this?".
If you say no you can pick up your car and go somewhere else. It's not that the mechanic is taking on the risk of an oil change turning into a full engine rebuild. They're simply required to announce what they're going to bill you for before they start work.
That way if the mechanic say, "It'll be $500 for me to change your cabin air filter." you can find a new mechanic.