I have never had a fish shipped with ammonia burn, and I have rec'd plenty of fish shipped, even one lost for a full day by FedEx. I feel like it can be easily avoided, easily. I am not convinced this is ammonia burn, the other fins and fish seems alright otherwise, and if during transit the fish crapped so much it caused a burn, it would likely show some signs of ammonia poisoning no?
If the fish was shipped with oxygen, which it should have been, ammonia burn from transit is not super likely because, it is my understanding, the PH drops to the point that ammonia is far less toxic/harmful. It is only once the bag is opened and there is gas exchange that the PH rapidly rises causing any ammonia to be harmful, which is why you only temperature acclimate fish that were in transit for longer periods of time but you don't drip acclimate them like you usually do. Maybe OP drip acclimated, maybe not, but I feel like if anything this was just a problem that was compounded, and not the cause of the OP personally. I know I wouldn't be happy receiving a fish like this, but if this is a fish I wanted forever, etc. I would likely just suck it up at treat conservatively.