If you sell off overstock items on a sales order (or service ticket) eAuto will then show usage on that item and eAuto will suggest to restock it. You can write that inventory off but then have a difficult time bringing in a check with nothing to attach it to.
The reverse PO will not show usage, reduce your stock and when you receive the reverse PO you can put cash to it.
Here's a screen shot of how to create a reverse PO so you can return an item to a vendor you did not purchase it from. Create a normal PO. Pick the vendor you want to return the item to. Instead of putting a positive quantity for the item on the PO, you put a negative quantity. It serves the same purpose as an RTV but you can use whatever vendor you want.
. Once you receive the credit for this type of PO, to receive it you need to change the type to Return/Receive in order for the item to show up to receive it. Then you will have a negative quantity receipt that you can use to create the credit memo off of that the vendor sends you.