If you can afford it, go for it. I would not do it in your shop, use your shop as advertising.
Bash away, but i like petsmart, or the fish part, and heres why, and i am sure aside from diehards, joe public does to.
It is clean. There are alot of fish. The tanks look clean. You dont see a bunch of nasty filters and sumps, and it doesnt smell. Ours has a nice tear tank setup just for plants, very cool.
All fish stuff on one isle. Best of al, you geta good price. May be some crap products, but hey it has made walmart millions.
what i dont like about LFS's. And i have been to a bunch all across the state, checking them out, for ideas and supplies.
They are ussually cluttered. last one i was in had chemicals in three locations?? My guess is they are experienced folks, and thought anyone coming in should nkow chemicals for ponds are differant them aquariums, whatever.
As has been said, they are smelly and loud. Ferrets and birds.
They never have the dime store little stuff I need. Ie i was looking for some simple plastic airline T's. Not lfs, petco or petsmart i went to had them. Walmart at one town did. So you have a walmart, so make sure you have what they have and price the same. You could still have higher end stuff for real fish ppl, but you have to compete with walmart too.
I think a FISH store would be great if run by ppl who know fish, the store is celan and orderly, and they have the bargain stuff as well as the high end stuff.
One other thing that drives me crazy. Fish mixed up all over the place. mixed tanks. the ppl can never get the fish you want that way. would be easier on them, if you had a neon tank, a zebra tank, etc etc. havesmaller tanks dedicated to each fish. Larger tanks for display.
Make sure anyone working there is not giving out bad advice, or trying to sell a product. My lfs just convinced me i needed 2 chinese algea eaters, then all i hear on here is to get rid of them. Also i asked for otto cats for a tank with brown algea, and was told they would not help, when you can type in brown algea and otto in google and get a thousand hits?
I would have a computer setup, and if you get a question your not sure, you can search mfk and other sites, WITH them. Or even use it to show them what others say about the advice you have given. Never BS.. i have bought plecos for years, no one ever told me or asked me if i knew they would need food other then just sucking around your tank.
I say do it, but put the work in getting it right. Location, and setup. You can even have some stuff setup to display, like A sump, refuge, or the like, gett them asking questions, and let them know you are passionate. But your main filtration, and i would have a pro type sign board explaining what it is and does.
i could go on all day about this, i wish someone close to me had this interest, i would love to get involved.