This article will focus on how to use the SKU with a few different API's (GetItem, GetMyeBaySelling, GetSellerList) to track or find you items by SKU
Prerequisite - make sure when you add/list your item you are setting the InventoryTrackingMethod to SKU, http://developer.ebay.com/DevZone/XML/docs/Reference/ebay/AddFixedPriceItem.html#Request.Item.InventoryTrackingMethod. If you do not do this you will not be able to track/find you items using SKU.
There are 2 ways to pull up the items using the SKU,
1. You can search for each SKU individually using GetItem or GetSellerList
2. You can get a list of all your inventory and check the SKU associated with each item
A. Can I revise an exisiting item and set the InventoryTrackingMethod to SKU? (NO, you will have to end and re-add your item setting InventoryTrackingMethod to SKU)
B. Can I enter a SKU and get all the items using that SKU? (NO, if you are using InventoryTrackingMethod set to SKU, you are not allowed to have multiple items using the same SKU. If you are not setting InventoryTrackingMethod to SKU, you can have multiple items with the same SKU, but GetItem for example will pull up the newest item listed with the SKU)