Twitter is helping e-commerce merchants, like eBay sellers, to connect with their customers, understand their needs, receive regular feedback and generally drive up sales by influencing customers through building a personal relationship with them. There are certain ground rules that have to be followed when using twitter, however.
First, the merchant has to choose an appropriate username and create a relevant profile. The merchant has to learn to listen, interact, influence and provide content that is both entertaining and relevant. Using short, direct messages and answering questions are also important. Providing regular discounts can help too.
eBay sellers can use Twitter to advertise their products and influence customer choices to increase revenue. The increased revenue is, however, likely to take a hit from high shipping costs. To help reduce them, eBay sellers can use the Adship eBay program. Adship lets sellers make money through ads placed in the order-fulfillment process.
Read more about it here.

