According to a 2006 ACNielsen study commissioned by eBay, 1.3 million individuals used the site as a primary or secondary source of income worldwide. The figure for the United States was around half as many. But the study didn't parse out how much money each of those 1.3 million individuals make, or how many of them use eBay as their "primary" as opposed to "secondary" source of income [source: Gross].
How much will you make? I think my best month with Google AdSense was almost $5,000 over the last ten years. That amazing month blew my mind since it was actually near the beginning of my blogging journey. When you go from making zero to $5,000 in a month, that will rock your world. For me, it also got me even more excited because I knew there were other ways to monetize.