Trusted the people at the store for info instead of doing my own research. Now I know better . . . even the lfs, which is pretty decent, occasionally makes some dumb mistakes (for example, they have Endler's mislabeled as "Lender's," and literally don't know the difference).
The chain stores, of course, are considerably worse. I started fishkeeping by letting my little girl pick out one betta from Zamzowe's. The employee there assured me that it was one of the only fish that would survive in my house just fine without a heater. Well . . . the poor thing got ich and died before the week was out. Zamzowe's replaced it, hassle-free . . . and that one died three days later. When they offered to replace the second fish, I just gave up and walked out. We didn't try keeping fish again for a couple of years.
Now I know that bettas need room temperatures considerably warmer than the ones at our house (67 during the day in the winter; about 65 at night). How hard would it have been for the employees there to have done that much homework, instead of just offering to keep replacing the fish indefinitely? Grief!