Good thing I did not know this when I started.
My first dozen buyers got some really great deals and I had a lot to sell, so that was all behind me very quickly. My first hundred sales came in less than a month, but I was in a selling frenzy.
But, to address this issue, the best way to start out, today, would be to make a lot of small purchases. There are a lot of sellers, especially Chinese sellers, in my experience, who post positive feedback immediately after you pay them.