To be honest, I haven't really explored this possibility in detail.  I see the potential for shenanigans that could mislead the holder of the escrow account and lead to an unfair judgment ("Yes I signed for the shipment but there was nothing inside ...").  I would rather establish a personal relationship with the buyer.  I'd be willing to sign a notarized contract if requested.

That said, if you have a link to John K's terms or something else that works for you, I'd be happy to consider it more closely.