We have asked the question to the manufacture with the reply.
On visual inspection if you can see vice marks on the diameter then a crushing force was used via a vice (most would use wood blocks so not to leave marks and damage the finish) so no marks would be visible.
Over filling without viewing the customers own gauge they fitted and reading off the scale they would be reluctant as you can expect to give the supplier this. If looking for a refund on the item.
Over tighting. As a previous poster has posted the standard cylinder supplied via Weihrauch the gauge end and valve end are usually very tight to remove giving the impression they should be tightened up to this high torque when refitting, high torque is not necessary as the air in the chamber will seal the fittings in place. High Torque can twist the cylinder and weaken its structure.
Crossing of the threads Damaging the Valve / Gauge end when striping the old cylinder or corrosion resulting in the ends being very tight to screw up and using large amounts of torque. The thread would not be able to be checked when split open customers fittings/they would be reluctant as you can expect to give the supplier this. If looking for a refund on the item and aware they were hard to screw in.
This is one the main reasons we have stopped selling the tube only option there is too many factors to go wrong, having the right tools / experience / and safe way to test the cylinder after being built is a risk we are not willing to take. We sell them to Gun shops that are qualified to take the task on. However we feel it is too dangerous. We would like to see other suppliers follow suit or offer a service where they can send the tube to be changed at there facility so it is correctly done and checked safely.
Our complete cylinders are built tested to 260 bar in house before shipping, and then step back to 100 bar over night too check for leaks. Item will arrive to the customer with 100 bar present. If this is not the case then the tube should not be used due to damage in transport or a leaking issue. There is no need for the customer to take or alter anything on the cylinder and taking the cylinder apart can be detected by the manufacturer when sold as a complete unit.
Hope in anyway this can help.
Best Regards
Fenton Shooting