eBay prepared a guide for its sellers on "social media selling," advising them on how to use social media sites such as Facebook, Twitter, YouTube and blogs to promote their eBay listings. "Stories abound of how messages (on social media sites) have been propagated out to hundreds of thousands of people in just hours," according to the guide.

eBay explains in its overview, "in a nutshell, Facebook is for staying in touch, Twitter is for "breaking news," blogs are for telling the story, and YouTube is for videos." And it warns sellers to "genuinely contribute to the conversation," "don't spam your fans!" and "don't be controversial."

Some examples of eBay's advice for online sellers include the following:

Facebook: Use the Facebook Questions feature to ask your Facebook fans questions on what inventory they'd like to see.

Twitter: Announce new items, a new promotion, a new post on your blog, or news about the type of products you're selling.

Blogs: Use keywords wisely. One of the most powerful aspects of blogging is the ability to raise your visibility in search engines. Make sure you include the right mix of keywords related to your ebay business in your blog posts, but using them inappropriately could result in search engines giving you lower visibility for "keyword spamming."

YouTube: If the items you're selling are complex and require assembly, there's no better way to win customers' hearts than to have video demos on how to assemble your products.

eBay also advises sellers to post about their listings on their fan page instead of on their personal Facebook page and to create a Twitter handle separate from their personal Twitter handle for their eBay business.

"Mention your Facebook page in your customer emails and other customer touch-points such as your blog," eBay advises. "Encourage your customers to Like your fan page to stay in touch and get the latest updates about your eBay listings and deals."

Visit the eBay Social Media Selling guide to read more of eBay's tips.