and thanks for giving us some more details... sorry that this is turning into such a mess...
I'm a bit confused about how it was decided that the diver should be paid $450 for the animal in the first place... although if he was torturing the poor animal to death, and that was what he asked to give it up, I can understand the rationalization.
I think in the bigger picture, the main concern is that very few people are qualified or equipped to give a nautilus a comfortable home, so as you've read, a lot of the folks here really don't want the precedent that these animals should be sold to hobbyists. I'm not sure what the right thing to do is for the animal, and for the good of nautiluses in general... if this encourages people to collect them and sell them in the pet trade more by having people realize that they can get $450 for them, that'll be incentive for people to capture them. But it does seem unfortunate if you and your boss are penalized $450 for trying to do something responsible...
Maybe we can brainstorm a bit; what does the NRCC do when obtaining new nautiluses from collectors? I'm concerned that if we try to find it a good home, since you don't seem to have much respect for this collector, that it could be carrying pathogens or parasites. If it's unhealthy, it might be a liability. If those aren't concerns, there are folks here who are equipped to keep nautilus: gjbarord, Robyn, and I think maybe jhemdal. But I have no idea if they would want to risk bringing a new animal of unknown history into their tanks, and I doubt any of them would pay $450 when they could get one from the NRCC for $190. Of course, it's possible that the mystery ebay bidder is actually a good home for the animal, but that seems unlikely...
Unfortunately, sometimes when this sort of thing comes up, the best course of action in the big picture seems to be to make sure that the animal dies in the store without being sold, so that in the long term the stores don't buy them from collectors and the collectors stop collecting them. But that seems needlessly cruel to this particular animal.
Really, the diver overcharged your boss, and that's going to be hard to fix.
I guess some other things I'm unclear on are where the animal is now, and what we know about its condition and history... if the diver you got it from took such bad care of it, I'd worry that it may not have much time to live, which would make it even less likely to be worth $450...