1. Who is talking about unauthorized repairs? I am talking about repairs that are authorized, by the owner of the product, because who else would possibly have the authority to decide who is allowed to do something with a thing, such as repairing it, if not the owner of that thing?
2. Who says the vendor should be responsible for damages caused by repairs not done by the vendor? I was responding to someone who said that a repair not done by the vendor should void the warranty. Warranty only covers defects caused by the vendor, thus what they suggested was that vendors should not be liable for defects they themselves caused if someone else has repaired their product.
Warranties only cover manufacturing defects, not damage caused by independent repair. Voiding warranties for independent repair means that having such repair done to fix one problem voids the manufacturers responsibility for any unrelated defects.