For Fixed Price items, if you relist within 7 days after the item ends and if there is no price increase, change of title, category or item condition (new/used), the new listing will continue with the latest 7-days sales records of the previous listing.

In  Best Match, the higher the 7-day and 60-day sales records an item has, the higher the exposure will be. IIt is suggested that you use a multi-quantity listing to sell several items at once, as you will receive a boost in search results as your items sell.

For details, please view: 
http://pages.ebay.com/help/sell/searchstanding.html#build
http://workshops.ebay.com/thread.jspa?threadID=140000106