While we do try to make sure employees are trained, there are some things in our way. Among them is pay ( I make 10.75 as a supervisor, and that's just because I'm 23 with a college degree), stress (customer service fluctuates depending on how many customers there are or if there was a particularly difficult customer recently), and experience. While it would be nice to have every employee know everything, there is a thing called learning and people can't be expected to instantly know everything about fish upon walking into a new job. I mean, when you first began your job (your being respective to all ppl in the world) did you instantly know everything about everything? I bet not. For that case, do those of you who have been keeping fish know everything about fish keeping?
I have had many the customer who comes in going "my husband wants me to pick up the fish, but i forget the name..um...its...its small...and long...i think its that one...). Not saying this is what she did, but I also don't think the employee is attempting to sell you the wrong fish or deceive your wife on purpose.
I also find it hard to believe that these errors only occur at chain stores, as is so often implied by threads like these.
You could always try taking the fish back, explaining that it was the wrong one. Normally people are pretty nice about it.