I've seen people with real problems spend countless hours troubleshooting a bad alternator for them and paying for shipping it back and forth because mechman refused to believe the problem was their alternator. When I was interested in buying an alternator I emailed them in hopes of learning that they had since modified their procedures to be more accommodating to those with legitimate issues. Never heard back. The last thing I wanted to do was drop a lot of cash on an alternator and worry about the possibility of running into problems and wasting hours hassling to get it fixed.
Understandably, there are people who do not know what they are doing, but when I considered the sheer amount of time and attempts it took for the alternator to finally get fixed I was pretty disconcerted to say the least. Alternator manufacturers are not scarce for GM engines.