eBay said it will be conducting random "second category" testing within the next few weeks on eBay.com and eBay Canada. For those categories that overlap significantly, a seller's listing may appear in the second category at no additional cost. Normally sellers are charged two times the listing fee for listing in two categories. During the test, any second category will only be added after the listing has been fully submitted, regardless of listing method.

In some cases, eBay will refund sellers if they had chosen to list an item in two categories when eBay would have added the second category to that listing for free. However, the test is limited, and sellers who place an item in two categories should expect to pay the extra fee as normal.

Sellers will see a small notation at the top of their item page if a second category was added. eBay said having a second category added for one listing does not guarantee it will be added for the next listing.

http://pages.ebay.com/help/sell/l2c.html

http://www2.ebay.com:80/aw/marketing.shtml#2005-02-28114225

http://www2.ebay.com/aw/marketing-ca.shtml#2005-02-28175415