Notwithstanding the merits (or lack thereof) of such a decision, is there a limitation or prohibition that would stop a County Sheriff from selling firearms that have been seized under Article 59 of the CCP? Assume that the Sheriff will comply with all of the formalities for a sale of seized property contained in the local agreement between the DAs office and the SO.

Sometimes the judgment of forfeiture has a restriction that the items forfeited are for destruction or use by the law enforcement agency. If there is no such restriction, I guess a sale is possible, although I share your concern about doing so.