-Have lots of cute harness vests. I find it easy to find "clothes" but not so easy to find the great harness vests like several vendors sell here on this site. You might even contact a few of them about wholesale. Leashes to match too!
-I think a really good seller would be to have outfits made up with local high school and/or college colors. We are fiercely loyal to our local HS Panthers. Anything with their logo and/or colors would be a sure sell. I am sure other schools would be the same.
-Hair clips that really grip fine hair
-Premium dog food -- like Canidae. I have to order mine online
Find out what is not available in your area and become "the" place to get it. I drove to a nearby town JUST to get some Canidae (over a toll bridge too!).
-Quality carriers. I was in a small pet shop the other day and she carried Petflys. Had a nice display. I wonder if Celltei wholesales? I have never seen them in stores.
-Water bottle stands
-Quality grooming equipment -- like the CC brushes and combs, Wahl Peanut for trims, Good Andis Clippers, etc.
-Quality pet grooming products -- like Coat Handler, Plush Puppy -- not just the shampoo and conditioner but also products like the Swishy Coat and Topknot Gel.
-Unique dog beds. I am still looking for one like my DIL bought at a Walmart last year. Looked like a little couch and the seat folded out to have a larger area for play. I have looked at every Walmart we've seen but they must have been a one time deal. Just an example, but I'd look for unique ones that can't be found easily.
-A section for the dog lovers too. I have seen cute purses with dog breeds on them, T-shirts of course, but small items like wallets, checkbook covers, coffee cups, keychains might be good.
-Gift baskets for pets. Premade gifts sets packaged pretty in a basket or water bowl, or pet frisbee, and gathered under cellophane with ribbon.
-Don't foget the bobos!
And some great home made treats.
I don't ask for much do I? LOL! We really do not have any pet boutiques around here. I think it would be an excellent idea. Petsmart is okay -- but a more personal and unique store would be FANTASTIC! Good luck on your venture -- lucky Texas folks!