Bringing Used Equipment Back Into Inventory
You can bring equipment back into inventory via sales order / credit memo or via PO. Best Practice is bring back via PO.
Add the equipment to the PO using a -1 for the quantity. If this was a leased machine and there is a buyout associated with it that you will have to pay the leasing company for, then input the buyout amount as the cost on the PO. If there is no buyout then leave the cost as 0. Once the PO is received it will bring the machine back into inventory at the cost you specified on the PO.
Usually a deduct from invoice buyout is wrapped into the new equipment deal and is recorded on the sales order for the new equipment using an expense line item for the buyout. If you want to record that cost against the returned equipment, then do an inventory cost adjustment against that equipment for the amount of the deduct from invoice buyout. You also could have the expense line item used to deduct the buyout from the new deal point to the inventory cost adjustment account you use to do the cost adjustment against the returned equipment. This way the cost of the buyout shows on the returned equipment but the amount on the GL account for the adjustment is a wash. To use the overfunding to pay the invoice that brought the returned equipment back in, you will want to create an AR Misc Charge invoice or debit memo for the overfunding amount and apply it to the invoice you recorded the overfunding against. Then create an AP vendor credit memo and apply that to the invoice used to bring the equipment back in. The same GL account should be used on the AR and AP memos so the amount will be a wash against that GL account.
To capture the costs of refurbishing the machine, use the Inventory\Production\Refurbish feature in eAuto. This allows you to add the costs of parts\supplies\labor to the cost of the machine and reduce your inventory for the items used at the same time. Using this feature will give you accurate costs on the sale of the machine.