Uhm, I'm pretty sure that if you don't like it, you wouldn't shop there. Especailly if the fish are "peppered with ich" like you say.
It's PetSmart policy to ask what they're buying for, and its better to get an idea of what customers are shopping for, rather than sell them an arrowana for a 10 gallon (for example), then having it die, then mad customers. Maybe the employee was new? Usually newbies learn what goes together, and until they're there for a while, they don't know what all goes together.
Just calm down. What if someone sold you a fish that would have killed all your other fish? You'd be here berating the store that didn't bother to ask.