SPAM - RFC from list admin

I have noticed a few pieces of spam lately on the list. Our mail server checks all the normal relaying databases, so that has kept most of the spam out for ages. However, now a few have trickled in and it bugs me a bit. In the past it has been suggested that the list be closed - ie. only subscribers could post to the list. I have always avoided that because fairly frequently someone will post from a non-subscriber that they have equipment available, and I don't want to take that opportunity away from the list. I see two options: 1) I can close the list from non-subscriber posts or perhaps 2) I can require non-subscriber posts be approved before I send them to the list I would prefer to do number 2 above. However, this does give me the ability to occasionally see available equipment before the rest of the list. Of course I wouldn't abuse this, but - I don't even want that perception. So.... advice please? Regards, Jay Wests