This has nothing to do with whether or not one has faith in one's own work.  Rather, it is a matter of what an abstract report is and is not.  I am certainly no underwriter, nor is it my responsibility to clear any potential clouds on the titles to the properties I search.  I merely research the available and properly indexed public record and compile a report based on those findings.  An abstract report in and of itself should never be construed as an opinion of (or warranty of) marketable title.

Using your analogy of the auto mechanic, the disclaimer should go something like this:

"The brakes on your vehicle were repaired by a skilled technician using factory-recommended parts and will function properly in accordance with the manufacturer's specifications under normal driving circumstances.  We will assume no liability for their failure, however, if you decide to enter this vehicle in a NASCAR race or a demolition derby."

Of course, common sense dictates that our daily driver isn't quite the same vehicle as Dale Jr.'s Number 88 car.  However, in the case of title abstracts, disclaimers can be a useful tool when the distinction is not always quite so clear.

Regards,
Scott Perry