Making a great online dog supply store.
There are a ton of pet supply stores on line now and not all offer great quality or selection on their sites.
The best on line dog supply store I saw offered unique and unusual items specifically for dogs. They had things that I have not seen anywhere else on the internet, and I get around, let me tell you.
One reason they probably offered such great stuff is that they only offered dog products, not cats or other animals. They also did not offer foods or health related products, but only accessories like bowls, beds, carriers and other fun stuff like that.
Maybe a niche market really is the way to go when you start a business on line