Yes, there is a lesson here that all of us must learn, and we usually learn by making a similar mistake. I did. The lesson is, never acquire any fish without fully researching the species. And unfortunately store staff generally do not know themselves, so do not take their word for it unless you happen to know the individual's education in fish.
A few years ago I saw a tank of "loaches" in a local store, and having never seen them before I asked the employee about them. She said they remained very small (they were scarcely over an inch and swimming frantically all over the tank, not surprising given the stress of store tanks on fish) and peaceful. I got the scientific name off their invoice (the owner knew me well enough not to refuse) and I looked them up at home. Good thing I did. They got considerably larger, needed a group, and had a rather nasty disposition as they matured. Had I bought them, they might or might not have taken them back, but that would have been even more stress on the poor fish, or I might have been in the position of having to euthanize them.
Always research the fish, on forums like this one or reliable sites like Seriously Fish. I have one local store, one of the better, that has a terminal in the store for customers to research fish.