We guarantee your car will be fixed right, on time, and within budget.

That is a common statement in the auto repair world. It sounds great, but how realistic is it?

In my opinion, the requirements to complete a job can only be known once the car has been dismantled enough to fully understand what's needed and how much time and material will ben required. The hard truth is, we are in the business of repairing things, and just as in repairing people, there can always be surprises and complications.

Motorists often misunderstand what we can know. For example, we look at a car with worn tires and we say, new tires are $xxx. It seems simple to price out tires, mounting, and balancing. But what if the tires are dismounted and one of the rims turns out to be cracked?

Suddenly we have a $500 complication -- a new rim is needed. We can't put the broken rim back on the car because it's unsafe, and the motorist is left with no choice but to buy a new rim.

Most shops would have quoted a set of tires without any teardown at all. And they would be very likely to have a customer relations problem when the broken rim was discovered. This is not a common occurrence -- 99% of tire repairs proceed smoothly. But it can happen.

The question is, what do we do about it? In my opinion we start by setting the correct expectation. We tell people that tires are $xxx, but there could be surprises. The rim is one example; as cars get more complex the service complications become more numerous and more common.

You don't get a promised cure at a guaranteed price at the doctor's office. Why is car repair different? It's not, but people mistakenly assume it is. To a large extent that's because mechanics set unattainable expectations and then they allow themselves to be painted in an unfavorable light for not living up to an impossible standard.

The way we correct that is by being clear what we can control in the offered service, and what we can't. Tires are a commodity; we can quote the price for different brands. Mounting is a standard service too; we can quote time to mount tires on the rims we see. Most of the time, that's all that's involved in a basic tire job. But when we give the motorist those figures we have a duty to inform them of the possible complications. Some will say, what's the worst case? That's impossible to answer most of the time. In medicine the worst case is, you die. In car repair the worst case is, you need a new car.

99.9% of the time those dire complications never come to pass. But people get old and die, and so do cars. The outcomes will not always be good. The best we can do as service managers is to disclose what we can, and paint a realistic picture.

Doesn't the customer always have the last word? That can be a misconception. Take the example of the broken wheel rim. Once discovered, we cannot undo the discovery. The customer may say "put it back like it was" but we can't. The forces to mount and dismount the tire may turn a cracked rim into a cleanly broken one. There may be no path but forward, and the only choice the motorist has is to buy a new or used wheel rim. Using the rim he arrived with may simply not be an option.

We may take one thing apart for repair, only to see another broken thing beside it. If that broken thing is a possible safety hazard, we place ourselves at risk if we do not fix it, so the customer in that case does not have the ability to decline a repair that would compromise safety. They can of course halt the whole job and tow the car away, but that does not do them much good. The newly discovered safety hazard becomes part of the current repair cost, no matter who does it.

The only options then are abandoning the car, fixing it now, or fixing it later. At one time cars were simple, and "fix it myself" was an option for many owners but with today's need for dedicated test computers and special tools it's a rare owner who has that option.

Here's the hard truth: Taking a car apart to evaluate damage may render it inoperative until fixed. Hospitals warn patients in advance when they undertake risky procedures. Those of us in the auto service business have a responsibility to do the same.

Another common situation is the multi step repair. Here's an example: A car comes in with an inoperative oxygen sensor, and the check engine light is on. We see the failed sensor and replace it. A week later the light is on again. This time the newly repaired oxygen sensor is sniffing an out of range condition, and we repair that next. It was not possible to see repair #2 without the prior completion of repair #1. Whenever we repair engine lights we always warn motorists that more than one round may be needed because there are a thousand things that can illuminate that simple light, and they may reveal themselves one by one.

If this sounds complex, costly, and scary, I agree! Yet it is the world we live in.

From the shop's perspective, our duty is to keep our training up to date and make sure we have the latest tools for the jobs we undertake. We need to use our best abilities to diagnose vehicles, and report our findings promptly and clearly. We need to be at the top of our game, and do our level best to get good outcomes. At the same time, we have to be clear to our clients with respect to what may go wrong and why, and what we can do.

Cars are complex and service is specialized. Not every mechanic can fix every car. In a big shop like hours there are techs who specialize in certain brands (like BMW,) and others who specialize in certain procedures (like convertible tops.) Knowing what we know, and what we don't, is always a challenge and an exercise in humility.

John from Massachusetts