Like most chain stores and some LFS, like my job, we have brief descriptions of the species such as the scientific name, temperature requirements, max size, behaviour and occasionally tank size requirements. I believe all shops selling fish or aquatic species should follow this going the extra mile of mentioning pH, diet requirements, origins, etc.
They could also have the common compatibility charts, it wouldn't be difficult to research and make a few of these charts to hang up around the store.
That why, customers won't return to the store complaining about their new fish killing their current fish. Unless that was the idea to get them to come back....
But what I'm saying is fish shops should have more facts stated around the store, or like most chain stores, pamphlets to be taken.
This next idea might be a little on the expensive side, but I think instead of selling the fish in bags only, it would be nice providing little boxes just big enough to fit the bags in. That way the ride home for the fish can be less stressful and the bag is better protected from popping. I tend to do this for every new fish I purchase, I always bring a little box, lined with a soft, thin rag. In fact, my store sometimes will provide a box for customers purchasing a lot of fish.
Keep up with updating: most or pretty much all chains store have websites advertising what fish they carry, whether they're in stock or not. My fish shop always updates their website when they get new shipment in, this is where a lot of our customers come in looking for specific fish, plants or corals that we just got in or just ran out. This keeps the flow in selling fish a lot more smoother and keeps the fish from sitting in the store tanks for too long.
Presentation is everything... We've all been in fish shops where it's die off in all directions. Beginning to look like the employees don't keep eyes on the tanks too often... No one wants fish that come from bad looking tanks that appear diseased or tainted. Die off clean ups should be done before opening and before closing, as well as cleaning up when noticed, obviously.
All fish shops, or even just any pet store in general need to have a balance of business and proper livestock care. The better the livestock, the better the business. But of course it all sort of boils down to how the employees go about their tasks, really. They're the ones that are in charge of selling and caring for the livestock. But some stores focus more on the business side than the general health and wellness of the livestock they're trying to get out the doors.