1. You can set up one account and name it Inventory Adjustment, as I noted above, and use it for Either direction (up or down $ changes).

2. Delete is not Close. Delete = Gone. Close = Done. Wait for the Accountant's Changes file to be imported, before trying to change historic POs, then.

3. If the Item was listed on the purchase, and the item had that account mapping as you now see, then it posts to COGS when it Sells.

"probably some negative items we will never sell again, so can I create a "bill" with the negative quantity and "0" cost? or use inventory adjustment with "0" value change and post on COGS account, after that, I can inactive this item."

Stop trying to make More Bills. There is no Vendor involved, now. You use Adjust Inventory to fix your inventory. You would not Create new bills; you would find old bills with bad data entered and fix it there, if you could or if you cared.