There are good, and there are bad mechanics unfortunately.
I do my own work, and I respect a mechanic that catches something I missed. I have however had mechanics (Canadian tire) which have sabotaged my vehicle(s). It is unfortunate, but it does occur. In my case, two different vehicles, two different locations - years apart even, and in both cases, my vehicles magically developed torn CV Boots on the drive shafts (though i personally inspected them as OK not hours before).
I've had a vehicle I purchased turn out to be completely unfit for the road - to the point of where months after having purchased the certified vehicle from a used car dealer, the MTO inspected my vehicle, and the technician and the sales persons both lost their respective licenses. The Dealer's brother was the mechanic which wrote an illigal safety. The vehicle problem was a rotted out frame (rust) which the mechanic covered with black tar, and wrote up the car as a pass. I got into a mild fender bender, and it did massive damage - that was what raised the red flags to get the car inspected proper by the MTO. Neither of them will work in the car industry for the rest of their lives.
Good moto and auto technicians are worth their weight in gold. If you want to do your own work, make sure you do good work. When it comes to a safety, I leave nothing for "interpretation" I prepare the vehicle to pass, plain and simply. I am a bit overboard though, locktite every bolt and torqued to spec, every bolt gets white paint, and green paint dots (White for locktite, Green for torqued) and safety wire where applicable.