Once you have determined that two items have different Internal ID numbers. (Stock Manager: Current Stock tab) then you can decide which one to keep.
It is recommended that you KEEP the one with the most purchase order history and the most sales history.
However, if you can choose to keep the one with a better description and better SKU numbers. The merge process will transfer and retain all pertinent information.
While highlighting the item in the Inventory Center, choose the "Item Activity" view on the left.
Here you will see if there are any pending customer orders, a history of purchases from your vendor, and sales history.