What qualifies you to be a 'gunsmith' in your country ?
Surely by any law / legislation a 'gunsmith' returning a 'wall hanger' (DP Rifle) to a 'usable' condition bears some responsibility.
In the UKwe have legislation that covers "fit for pupose", your gunsmith was returning this to a shootable rifle that should have been 'fit for purpose' but obviously wasn't.
This legislation covers any goods, from a pen to an automobile, to toilet paper - it is nothing to do with 'proof' testing or any other firearm legislation.
Surely in the US (I presume you are in the USA) you must have something similar ?