You can examine it to see how worn the action is... with the action fully open inspect inside at the top of the action where the breech bolt locks up... feel with a finger if there is a 'lip' of steel at the rear of the locking lug recess, as if the locking lug has pounded back... if it has been shot a lot this occurs...
Another thing to check (with out ammo) is at what point the trigger releases the hammer... with the action cocked and the gun not loaded, open the action using the release button... now with the breech bolt halfway back, hold the trigger in the fired position and very slowly move the pump ahead closing the action... it should hot release the hammer until the breech bolt is in the locked position fully up. Some time a worn gun will release the hammer before the breech bolt locks up if the hammer is held back. This model is capable of slam firing but it should not fire unless the bolt is fully locked.
Another thing to inspect is is how much the back of the bolt moves upward when the hammer is released... again with an unloaded gun, close the cocked action and and while watching the back of the breech bolt pull the trigger... the back of the breech should not jump much if any... one that jumps up a lot indicates a worn gun.
Another test is how the action release works... when depressed to open a cocked action it should also pull the hammer back and disengage the hammer from the trigger... So while the cocked action (unloaded) is closed, depress the action release and keep it depressed and pull the trigger. The hammer should not fall. Often this disconnector has been altered (or worn) and is not functioning correctly.
The Model 12 for a great number of years was overpriced. It a good old gun but extremely complicated and expensive to repair when worn. Being a reblue/rework/restock I think you paid a fair price if it all checks out per the tests I mentioned above.
I forgot about the safety... when engaged does it block the trigger pull correctly and when disengaged after testing still hold the gun unfired?