Since the OP didn't know for sure what was stressing the Jawfish, all options were on the table. Heavy breathing is a symptom of just about anything and everything - crypto, oodinium, flukes, ammonia poisoning, etc. Doing a f/w bath was a shot it the dark, but since the Jawfish seemed to just be getting worse and worse, it was still better than doing nothing at all IMO.
I guess in retrospect, I cannot disagree. Flukes was not likely. Oodinium was a possibility. Ammonia poisoning was also possible with the strange shipping technique.
To the OP: Sorry for your loss. As others have already suggested, demand a refund and never do business with these clowns ever again. Call the BBB if you don't get satisfaction and let others know on here about your experience with this vendor.