This is a very common way to promote offers. For example, you will often see a blog post with links to certain products or services. If the reader clicks through and makes a purchase, the blog owner will make a commission. These in-text links blend in with other content on your site and are a great way of promoting an offer within your content, without being over-the-top salesy with banners.
Ebay is a bellwether. It's been around since nearly the start of the online boom. But, like any other platform, success can seem fleeting if you don't know what you're doing. Selling items on eBay, professionally that is, can be an art form. Getting people interested in your auctions isn't always easy, especially when there's hefty competition and low demand for what you're selling.
The problem with affiliate marketing, like many other home business options, are the so-called gurus and get-rich-quick programs that suggest affiliate marketing can be done fast and with little effort. Odds are you've read claims of affiliate marketing programs that say you can make hundreds of thousands of dollars a month doing almost nothing ("Three clicks to rich!"). Or, they suggest you can set up your affiliate site, and then forget it, except to check your bank deposits.