Somehow the KVRaudio.com forum, with thousands upon thousands of visits and members manages to have a classified ad section, without spam.

It's here for those that don't believe me. http://www.kvraudio.com/forum/viewforum.php?f=43

It's also a place where folks share great music equipment/software deals. It has a nearly 'wiki' like self-policing. Somehow they get it done. I honestly don't know the methods by which they prevent spamming of the forum, but it seems like if there is spam there, it's heavily outweighed by legitimate posts.

What's odd about it, is that it's probably frequented by an equal number of US and European forum members, so you see lots of stuff for sale in Euro and other currencies.

I've sold a soft-synth through there that I won in the monthly song contest. I actually gave it up if someone could prove to me that they donated to the charity of their choice. I got a real mailed receipt from Oxfam, and mail from Oxfam still to this day. Sold it to a Brit expat living in Japan.

So, I think there's a way if there's a will - that can probably keep the spam away. I don't know how it rolls, but there is evidence of it working.