we need to have a little talk here...I would never want you for a customer....I'd recommend you see my nearest competitor.
The only thing that is off about the cotter pin is that it appears to be a bit small. Even so, the nut can't back off unless it shears the cotter pin.
The cotter pin is an easy thing to replace. Packages of cotter pins are generally less than $1 at the local Big Box store.
Frankly, I'd be more concerned about the damage on the Upper Control Arm caused by the hammer welding gorilla. Specifically, why doesn't the shop have the proper joint splitting tools? What other parts were "hammered"?