What is considered a low profit margin?

I am trading in beauty products and my profit margin is around 30%. It's a home-based business so no rent or salary or wages are included. I have experienced that my total profit is used to buy inventory. Is 30% profit quite low? Or anyone here is managing profit to make purchases as well as having some amount for a living? I am new to business so I don't have any idea. Your help is needed. Thank you!