Well, on one hand, I totally understand your frustration! Especially if you spent extra for special farrier care, that was a big waste. He could have suggested waiting for a couple of weeks before having any special shoeing done. But to give the guy a break, most abscesses occur in the front of the hoof, not in the heel bulbs and inermittent lameness in the heel area is USUALLY indicative of navicular issues. However, an x-ray could have helped differentiate the heel pain and a vet SHOULD do radiographs before diagnosing navicular.
The abscess may not have been "set back" though, so don't feel bad about that.
As far as charges go, I think with vets, unless the misdiagnosis causes more harm, such as death or preventable severe lameness, you just kinda have to pay him for his time and educated guess. Espcially if he just said that he thought it was nav. And didn't actually yet prescribe the shoes. Was he wanting to do more thorough exams in the future?(I hope) .Also, if hubby was the messenger, something might have been lost in the translation, so to speak.
In the future you could try another vet, or ask him to be more thorough, and hopefully you will get to be there yourself to ask the right questions. Luckily, the abscess blew out finally, and hopefully before the specialist farrier made it out and you can cancel that appointment and save that money.
I know it's really annoying, but at least it was that he guessed the worst case scenario and it was a minor thing that was actually the problem, not the other way around. I'd be more upset if he said it was just a bruise and there was an underlying problem he just didnt' want to mess with. He might not have meant you should start shoeing him differently right away or that he was sure that was the issue. I don't know since I wasn't there. But perhaps he didn't do more diagnostics since your hubby met him there instead of you.
Or maybe he is a lazy vet that didn't want to mess with it or he's really arrogant and overcharges. HEck, I don't know. =) But at least you can vent on here about it, and be glad your horse is already feeling better with the abscess healing up as you write.