Your using the exception not the rule to make a case. Simple case is the majority of belt changes are done to a correct standard, its only the horror stories that people cling on to. And besides, one done badly is quite easy to spot, lack of power and torque if done a little badly, obvious bad running if done really badly.because so many garages do f**k it up, either by not using the correct locking tools (the cheap ones are s**t and don't work) or not bothering with locking tools altogether and just muddling through (cos it's only a belt change right?)
If you don't have anything to show it was done by someone who knows what they're doing how can you say it's a decent job??