Free Traffic (or dead cheap traffic) comes from three sources:
1) Traffic exchange:
You have to surf other people's sites and they surf yours.
It is waste of time + bandwidth. If you don't buy anything from the sites you surf, why will people on the other end buy from your site? Autosurf programs have timers that change the page after every 20 seconds. I can say, these may be useful if you are displaying CPM (cost per impression) ads. However, the days when they paid $5 CPM are long gone. The hardly pay $0.10 per 1000 impressions now. It is only waste of time.
2) Automated bots.
Ever heard of a command called "ping" in DOS or Linux? This is what they do. If you ping a site, the counter (eg: statcounter, awstats, etc) registers a hit. And it may look like actual visitors.
It is waste of time to deal with someone selling this type of traffic. You will only lose precious bandwidth and end up with no human visitors, leave alone conversions. Your web host may even suspend your account because these bots puts two much strain on their servers.
3) Traffic from parked pages/ Redirects.
I will give example for this type of traffic. If you visit
http://www.keyboard.com/, you will find links to related sites. Now, if I want to buy a new keyboard and visit this site, I may click on these links and buy something.
If the source of traffic is links on parked pages, we can expect good conversions. This type of traffic is not cheap. It is almost equal to running PPC campaigns.
However, nothing beats search engine traffic. It is free and you get copious amounts of it. And as far as conversions go, it is the best.