serial used and purhase should come under serialized inventory
we normally sell both new and used stock. but when we check stock , we check serialized and then go back to used item and count one by one.
There should be a function which comine those or we can see how many one model we have in stock.
to keep track of our stock, i am adding supplier purchase and customer purchase under vendor. this makes a mess in the vendor list. this is not a good function. IF you need further explanation, please call me on skype.