Knowledgable staff, that actually CARE about ALL of the fish in their store.
Proper display of fish, and not having the tanks stocked to the HILT.
Clean tanks, and getting the dead-o's out of the tanks.
I also like to see when someone will write on the side of a tank "Do not sell - treating" which tells me that they actually keep sick fish in the store til they're healthy.
and LAST, BUT NOT LEAST (by any means) is the bettas.
If a store has horrid conditions for a betta, I will leave immediately.
Well, after I raise a ruckus and yell and scream first, then point out which fish need attention.
THEN i leave.