How do I match an item to eBay's catalog?

To do this go to "Items" --> "My Items" and click on the title of the item to edit it. On the "Marketplaces" tab enter your product identifier (such as the UPC) into the corresponding field near the top left of the page. Then click the blue "Catalog Match" button to the right. Next click the "Search Catalog" button. This will give you one or more matches to eBay's catalog. Click "Choose This Item" to the right of the correct item.

You can then choose to pre-fill the title and identifiers for all channels (eBay, Amazon, and the Vendio Store), or just pre-fill the title for only eBay, or pre-fill the title, identifiers, and eBay Item Specifics (show as an additional description) for eBay only. Once you are done click "OK". Your item is now matched to eBay's catalog.