From the website:

Shill Bidding is bidding that artificially increases an item’s price or apparent desirability, or bidding by individuals with a level of access to the seller’s item information not available to the general Community. Shill Bidding is prohibited on eBay.

Because family members, roommates and employees of sellers have a level of access to item information which is not available to the general Community, they are not permitted to bid on items offered by the seller – even if their sole intent is to purchase the item. Family members, roommates or employees may purchase items from a seller without violating this policy simply by using purchase options – such as Buy It Now – which do not involve bidding.

eBay strongly encourages sellers with employees to ensure that their employees are aware of this policy and the possible consequences of violation.