I keep reading comments that seem to suggest it would be better for the marketplace to "get out of the way" and only be a method of connecting vendor and buyer. Rather than re-inventing the wheel, I was thinking of just spinning up one of the many OSS clones of CL or use some kind of forums software. I don't really want to manage some stupid escrow service where people can get fucked over again. If the system is kept simple it'd be pretty easy to manage and cheap to host.
People really have no freakin clue what they want. The problem with darknet classfieds is that they get filled to the brim to scams.
Personally I like connecting with vendors I've been using for awhile via bitmessage, torchat, or xmpp. Then just working with them directly. I still think it's important to use the markets for initial or large orders though. Really I would be most interested in a multisig escrow service that was just there to act as a 3rd party for transactions in case something happened to the buyer or seller. (Like bitrated for tor)