I am Board Chairman of a non-profit museum here in Oregon.
We have a De-accession Committee that nominates items for de-accession. All items to be de-accessioned must be approved by the entire Board. They are first offered back to the donating individual, then to other non-profit museums in the area, and lastly sold through an independent third party with funds going back to the museum.
No museum employee or Board member may purchase any of the de-accessioned items.