Hi Catherine,
Ezbargins has given you some great tips and the links provided above should keep you busy! :) There is definitely a wealth of information here in the forum and if you find yourself still with a lot of questions, there's the staff and other members who are always willing to help out.
Pet products is a good market but I would also recommend doing a Completed Listings Search for a specific pet product that you are interested in selling to check your competition and to see how well it sells on eBay.
To do a Completed Listings Search, just click on the Advanced Search link beside the Search button. Green means sold and red, unsold. Note the sell-through rate and the average selling price. This is important because the wholesale price needs to be at least 20% lower than the retail price in order for you to make money.
Below are some of our verified and highly recommended suppliers of pet products.
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Hope that helps! Good luck!