I don't think I've seen/read any formal policy on this. Given that it's an Obihai product, which you own, and you simply want to find it a new home (you're not running a business selling stuff), it seems reasonable to me for someone to send you a PM if they're interested.
By contrast, somebody running an eBay-style Sanford and Son junk dealer, advertising a link here on the forum to buy and sell OBis, would be considered commercial spam.
