Actually I have been up to this for a while, and it still works. Best approach if you dont want to get flagged:
Post to 5-10 different cities (changing the text and title every time). Save those ten ads in notepad (for use tomorrow). Make sure each ad has a different email to send to. Most regular email services cap anywhere from 100-500 messages sent a day.
After the posts, leave for an hour... once you start responding is when people flag the ad, so take your time. After an hour come back and start responding with "sorry it took me so long, too many emails"...
Now the only question is, where can we find an email service that can autorespond after an hour, and the cap is about 10,000 emails a day? Then you will just have to post and kick back. So if you can tell me one please PM me...
This technique has given me a 20% conversion rate... the longer you dont respond, the more Shmucks will see your ad.