It's never a good idea to buy a fish that gets huge saying to yourself that youre going to upgrade. Most of the time this doesn't happen. We all like to think that we'll get a bigger tank in the future but it's not always gonna happen.
These fish need a minimum of a 300 gallon tank. And even then, they should be kept by themselves. Odds are youre not gonna upgrade to a 300 plus gallon tank to keep one fish.
I would opt out of the purchase. These fish should not even be brought into fish stores unless it is a special order for the rare hobbiest that has the necessary set up.
Bottom line is this fish will probably suffer regardless becasue your LFS made an irresponsible decision in bringing it in in the first place.