The rating problem is a common one of any auditing / assessing job. Too loose or too strict criteria prevent an actuarating with added value, as every factory will have almost the same rating at the end.
However too strict criteria present additional consequence. As factories can’t reach the expected level, they look for ways to turn around the problem. If the auditing process focuses on a final ranking (or certificate, or “pass” report…) then all is set for a vicious circle.
The factory hides the truth and might falsify documents. A compliant status follows after the audit, the customer can claim to be working with compliant factories, putting more pressure on (other) factories and auditing firms to get even more compliant reports.
This is clearly not related with the actual facility performance in terms of social conditions, but more with the facility’s covering-up skills.