My approach to this 'gray area' is the same. I feel properly covered by the CGA itself:
"Experience in the inspection of cylinders is an important factor in determining the acceptability of a given cylinder for continued service. Users lacking this experience who have questionable cylinders should return them to a manufacturer of the same type of cylinders or to a competent requalification agency for re-inspection."
CGA C-6 and CGA C-6.1 are the primary documents for steel and aluminum. The re-inspector is responsible for making sure he/she is always testing to the most current standard. The re-inspector is being paid to test to standards. Being overly cautious for your own personal peace of mind is not what the owner is paying for.
I am a newbie inspector. As such, I am overly careful about following the guidelines. I can Accept, Reject, or Condemn a cylinder. If the cylinder is clearly a hazard then I would condemn it and render it unfit for refilling. I was surprised at the amount of internal damage that a cylinder can have and still be serviceable by CGA standards.
There is a lot of 'judgment call' when it comes to cylinders that show internal damage. There are a lot of compromised scuba tanks in daily use and they aren't going off like popcorn on diver's backs. Statistics and my training tell me that the inspection standards are appropriate and should neither be relaxed nor strengthened.
PSI states that an inspector has no right to disable a tank with out the customers prior permission. Doing so can make the inspector buy them a new tank. You can write condemned on the tank but you can not render it unusable. The customer has the right to get a second inspection if they question your results and actions. They are denied that option once you render it unusable. Your agency inspectoin certification may say different but I invite you to call PSI for their supporting documents regarding the practice of rendering tanks unusable with out the owners written permission. There has been problems such as tap stops on a good tank being taken for cracked threads and being rendered unusable. Also instances where the wrong tester was used to electronically check for cracks. 6061 tank will fail if the older device used on the bad luxfers's are used. different alloy different machine needed.