...never throw out or sell a biner unless it just won't function at all. That is just my thoughts.
Training is the key Burnham. That is something that is sorely lacking in the private sector.
You're right.
But I can tell you that I did receive some training by a very reputable climber (who shall remain anonymous) and during the demonstration of fall protection caught his own mistake of a screw gate carabiner being all the way loose instead of tightened.
If a seasoned climber can screw it up (no pun intended >>> no, really!), then I surely won't trust that piece of gear. Ever.
No record of an accident caused by this = it's never happened ???