This ^. Plus I make sure there's no aphasia or visible pests like bristle worms or flat worms.I have a couple close to me that are decent. What I look for:
1. A decent display tank. If they an maintain a nice display tank with corals for more than a few weeks, they most likely understand what is the appropriate methods and have the possibility of applying this to their sales tanks.
2. They sell more than clown fish and invertebrates. If this is all they sell, then I would debate if they have the skill set to maintain a thriving ecosystem.
3. No dino outbreaks. I know these are hard to control perfectly..but if you are in there and they have dinos they are not paying close enough attention plus you will be importing dinos into your system.
4. No dead fish anywhere. I know this is obvious and you cant help dead and dying fish..but you can at least quarantine your sick fish in quarantine so that you are not sharing water. Plus, if you have dead fish in your tanks and your workers are just doing shelf stocking...I dont think they are paying enough attention to what matters.
5. Finally, a 'not for sale' rack of tanks. Be it quarantine, hospital, or just 'new arrivals', this to me is actually the most important thing. This tells me that the owner has a level of quality expectations that they pass on to their clients. Selling new fish that they just got in the other day means there is no accountability.
I live in a very large city, one of the top 10 largest in the US, and am lucky enough to have a dedicated coral shop 15 minutes from me that is absolutely amazing and a general lfs that stocks almost everything. However, if you were to go edge to edge of the city you'll only find that 6 out of the 47 "lfs" stores I've visited, all within a 4 month time span to help reduce any variations, are actually worthy of spending money at. The rest of them ranged from more simple aphasia and a few noticeable pests to absolutely horrid. Not joking here, about half of them had multiple dead fish in the tanks; multiple fish with glazed over eyes like they were blind or something; tons of ick and other parasites; aphasia all over frag tanks; dinos in most tanks and especially in the invert tanks; they reeked of rotten fish and algae... the list goes on. So, like others have said, it's hard to find good "lfs" and if your only good one is like 3 hours away then just make the drive.
I've never ordered online, but plan to this year. My plan is simple, just stick to well known and reputable places like BIOTA or something. (I'm getting a mated pair of Mandarins finally )