Billy, of course, is right...everything I've ever read about sea horses state even the hardiest, easiest sea horse species still need a tank free of predation, and typically a species only tank, with less circulation than a reef tank.
Even if you don't have corals, you need sufficient alkalinity to maintain a proper pH for your fish.
sounds like one of the most caring stores I've ever heard of. Even my LFS
here will let a person buy fish 24 hours after they buy a new tank, because they need to turn a profit to stay in business.
Perhaps the question isn't "how do you tell an LFS
they are wrong" and rather "how does one accept that the LFS
might just be correct"...