I think it's a great idea. The classifieds section is designed for legitimate members to sell their gear, not for to be an open forum for any and all sales. People who are looking for that can list their wares on eBay. I like the 2 month time frame, but think 1 month is probably a little more reasonable.
While your at it, perhaps we can add a one week time frame for new members on top of the 5 post requirements to be able to add links. If it's something important from a vendor or known source they can always pm the mods for immediate access.
Jack