I often wonder about LFS and how they stay in business. Most probably stay afloat with servicing tanks. My LFS is a great store, the owner has a degree in marine biology and has been doing it a long time. He drives down to Los Angeles every other week and brings back great fish from top suppliers. But, assuming he brings back 50 fish (I think he brings less than that usually), say an average price is $45, that's a gross of only $2,250 every other week. He's obviously paying his suppliers and his expenses.
He rarely stocks exotic or expensive fish (purple tang or Chevron tang is about as expensive as his fish get), saying that his customers aren't in the market for expensive (i.e. more than $100) fish. But he does sell corals and inverts of course, and I know some fish get returned and sold again.
I assume there is a hefty markup on dry goods and the occasional tank build for a doctor or something. Seems like a tough business. But thank goodness they are here! I've only bought two fish from LA/DD, and that was because my LFS couldn't find them for a long time, and I got impatient. I like to support my store when I can.
I noticed that even Vivid Aquariums now offers regular pet supplies. Actually, the pet supplies comes up first on Vivid's website now. LA sold out to Petco. The economics must be such that you need the dog food/grooming/kitty toys to keep the lights on. The Petco / Vivid model may be the only way.
And yet there are big stores that deal in huge volume. The Reef Lounge in Orange County is an amazing place. Thousands of frags, hundreds and hundreds of fish at any given time. Exotics, big small, rare, you name it. They obviously are going ALL IN, I wonder if they are profitable.....