Here is something I tried doing once. I would contact folks who are selling cars and houses on CL and offer to post their ad on 10 other free classified sites which are high on traffic for a small fee of $5. Even if 2 out of every 100 sellers take up your offer, then you are looking at converting near about 20 sales on every 1000 sellers you contact. You will find more than 1000 seller ads on all top 20 cities on CL. So basically there is a potential to earn near about $100 for every city you hit. Imagine if you can do that across 20 cities every day = $5 X 20 X 20 = $2000 per day. I know it sounds a bit crazy but tell me which of these things I've assumed is wrong:
1. Folks who are selling houses and cars worth thousands of $$$ will be willing to spend $5 to increase the chances of selling. Also, they don't consider $5 as a lot of money to risk losing to a stranger.
2. There are more than 1000 'For sale' ads per city on CL any day.
I've tried doing this in a very small scale and I've found more than 2% conversion on the contacts I made. But I was never able to scale up the method.
I hope this will help you make some serious money. Let me know if you have any questions on this method.