It's your job to research a fish's needs before you buy. You can not rely on the information from sales people. Please keep this in mind for future purchases.
You're right. That said, think about how many people on the site started out in the hobby this exact same way. I, for one, trusted the advice of chain pet stores when I set up my first tank. It's a trial and error sort of thing; your fish die and you start poking around for more info. I didn't even know that sites like AC existed when I set up my first tank, and it was so easy for me to assume that pet store employees would give me sound advice.
Aside from all this, it appears from the original post that the killi was a gift, and the OP is at least trying to learn about the species and do her best to give the fish a good home. Fortunately, I've never been put in that position myself, but if I were I don't imagine I'd have a better course of action than to post here and try to learn as much as possible.