Darn good question. I'm not sure as there's any policy on this one. Personally, while I'm not entirely comfortable with it, it may be Ok as long as the purchase price goes back into the same account (budget, other, etc) that was used to purchase the machine in the first place. Otherwise, it feels too much like money laundering.
Assuming it was purchased with budget funds, you could process it like the return of an advance. That is, the "donation" would be placed in the budget category. Be sure to run this (including the price) past the bishop as one of my concerns would be the appearance of selling it at too cheap a price as a personal favor at the ward's expense.
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