Fish store employees are like tech support and teachers. The good ones are the ones with a passion for the jobs, who truly care about the work. The same way I'd rather lose a sale than have an angry mother come back, or a kid left with a bad experience (I'm a theme park face painter, kinda stupid, I know but it's fun, and the hours work with my classes.), there are fish people who care to do the research on their own. And then there are the ones who it's just a job, and they're only there for money, which is a valid outlook to have, to be sure, but it's irresponsible when there are living things counting on you knowing what you're doing.
In that respect I can kind of understand how pet store employees get elevated to this 'godlike' state of omniscience, because the general public trusts the company to hire people who give correct information, because there are lives at stake; however insignificant some people may feel they are. The stores advertise experts, and there's a trust between store and customer to supply what they advertise.
If they do decide to go through with the pond, I'll have a bit of leeway in the supplies they buy. I suppose I could start with pointing out the big issues we had with my old tank and the pond at the rental( the filter was wrong and the fish occasionally got pulled through it. Most of them actually survived...). My dad's strange though, he gets stupid in love with his pets, he doted on those pond fish and loves our cats to death, but he has these bizarre arbitrary guidelines on what he'll do for them. Usually it's a time and/or money constraint.