Starburst/Sunburst Anthais

Depending how large it is now it might be fine for a while as long as you can keep it adequately fed.
Once it hits it's adult size I don't think you'll have enough room in the tank to give it enough swimming room. It might survive but I don't think it will behave naturally without enough room to swim which could lead to a decrease in health/increase in stress/more susceptible to disease/infection etc.

+1 on not trusting an LFS until they've proven to you that you can trust them and that they aren't just out to make a buck and actually have the livestock's best interests in mind always. Even after you trust an LFS it's always good to get more than one opinion on any purchase IMO.
Not every LFS employee is an expert on every animal they carry.

 

Thanks for the advice everyone.

The Sunburst is out and about when we are not around, I can tell because when I walk in it is out but hides if I come near the tank.

My question is how in the hell am I supposed to feed him?! He runs everytime I come near the tank and when I sprinkle in food the clowns gobble it up and the rest hit the bottom.