Hello Atcan Display Inc.,

Thank you for your questions! Have a look at this blog with Quick Tips for adjusting and transferring inventory in Sage 50 CA 

At the bottom, other resources are listed including KB 12805 on How to enter an inventory adjustment.

Also see the KB 13052 with details on how to delete inventory items with no quantity.

Hope this helps!
Erzsi

Hi 

First I think best to check what inventory costing method the file uses , Avg cost or FIFO?

then best find out if inventory is set to sell below zero, and how many item cost, value, quantity is inaccurate.  (for example if you have ten thousand item that is out, i think best is start over a new file might be better)

Avg cost and yes, allows below zero. 
We do have a need to view our history, we're constantly looking up old invoices (pre 2014) to see what was ordered, so as much as I'd get a deep satisfaction to blow everything away, it would hinder us way too much. Unfortunately, I also feel pretty comfortable in saying that nearly every single item is wrong (both cost per and qty, usually) and needs fixing, and we have around 600 items in use. 

This is very helpful! I looked far an article like this on my own and couldn't find it, so thank you very much! 

When you are using average cost for your inventory it will go wrong if you allow inventory to go below zero. This is something I try to avoid with clients if inventory is a major concern for them. (ie manufacturing or retail ) As soon as an item goes below zero the average cost will go wrong and it will not correct itself by adding more inventory. An adjusting entry would be necessary and the correct entry would require a lot of tracking outside of Sage 50. 

Inventory works well if you do not allow it to go below zero. It just takes better inventory control and purchasing lead times. Processing the paper work in the correct order helps tremendously.