Just because the callipers have had a rebuild does not necessarily mean that they were abused previously.
Brakes as a component are prone to some of the worst wear of any component in the car. Not only do they go through tremendous heat cycles, the various chemicals in the brake pads can eventually eat at the aluminium that many callipers are made from. They get hit by debris from the road, often submerge in water, get coated in mud... etc etc. Over time they deteriorate.
I've had a few hassles so far with the bleed nipples on my track car breaking... They do that when they're old. Getting them out usually requires a lot of hassle, as they are a much stronger material than the calliper, so you usually end up having to tap them with new threads.
Same with the mounting holes, though that does sound more like someone cross-threaded them when installing.
Needless to say, if they've been repaired it should be OK. I would possibly see if you could find out where the work was done, but it shouldn't be too much of a problem on a road car.
Though to be fair, I wouldn't run brake parts held on with helicoils on my racecar, as the forces involved are much higher than in a normal road application.