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].
Whether you have a website or are still dreaming up ideas for a blog, you can also look into affiliate marketing. With affiliate marketing, you partner with brands and businesses within the content of your website. If you mention a product or service, you link to that produce or service using a unique affiliate code you received when you signed up for that particular affiliate program. From there, you’ll make money any time someone buys a product or service through your link.