There is a book called Zero to One, written by Peter Thiel. Its about startups, but also business principles in general. I read it years ago, and one thing stuck in my mind which is extremely relevant to Amazon, specifically selling on Amazon. That is:

If you are doing a business that is easy to enter, or for others to compete with, they will, and very soon you will be pushed to the margin. What is the margin you may ask, in relation to Amazon. The margin is products that are easy to obtain, are being promoted by people on Tiktok, sold by the dropship scam companies, available at the .99 cent store or chain store, etc. The margin is being lucky to make a profit at all, or maybe single digit profit margins even before returns and overhead costs. If you get very good at sourcing and identifying opportunities, people will recognize this and just copy you. No profitable idea you have will last more than a month or two, and that rate is decreasing as information sharing increases.

Now, if you provide value, that is, source really good product that is hard to get, that people want, great service, maybe make your own products, or have an exclusive deal with some company, THEN, you will start seeing the profits and it will sustainable.

I say these things not to sound like a know-it-all, but to save you the painful years and years I had learning how to successfully do ecommerce.