We use the "Custom Label" field to assign a unique code to each product line. The code tells us which shop the item is listed in and if the item is Auction or BIN. And then just a sequential number on the end starting at "0001" and running up. Gives us a possible 9999 items we can track on any one code. You could vary it to suit your own needs. Or you could add it into your TITLE field too, but to do that uses up valuable space for keywords.

We can also upload sales electronically into MYOB based on this unique code. This can give us tax data and stock control in there as well.

If you sort your active listings by this field you can pretty quickly see where you have duplicates as they show up side by side.

But primarily we use it to assist in tracking & stock control & storage. This number also appears on our storage bins so we can easily find it when it sells.