I'm surprised to hear that pinfiring is still around. The last horse I had that was fired was a retired racing appaloosa that I had well into his teens and I used to jump and trail ride him - he also drove a cart. Never had a soundness issure but his cribbing drove me crazy - refuse to have another horse that cribs due to him. (That was back in the late 80's).
I've bought and sold a lot of horses since, but haven't come across a fired horse in the past 20 years. Hard to believe that your 3 year old was done.