I used to do freebie trading a few years ago. Freebie sites are basically GPT sites but it is referral based.
You have to sign up to the site and complete 1 or more offers to get the required credit. Then to get paid you have to refer someone to the site that completes enough offers to get the required credit as well. These sites usually pay from $20 to $100. The higher the payout the more offers you have to do.
In freebie trading you make a deal with someone to sign up under their referral link and complete the site. They in turn will pay you thru paypal 50% to 75% of what the freebie site pays them. If the site pays them 60 bucks, they will pay you 30 to 45 bucks.
After you complete the site you can then pay people to be your referrals.
All of this is usually done on a freebie trading forum. The deals are set up in whats called the trade manager which just makes it public who you are trading with and for how much payout. After the deal is done both traders get an itrader rating. The higher the itrade the less likely they are a scammer.
Almost all of the offers that you have to complete require a credit card. Most of them are cheap or free trial offers but if you don't cancel before the end of the trial they hit you hard with recurring billing.
Free credit reports, weight loss products, and stuff like video professor or blockbuster. All are free or cheap to try but video professor costs $180 if you don't cancel on time.
Basically you are ordering these trial offers, getting credited, getting paid, and then cancel the trial before the recurring bill kicks in. Unless of course you like the product and wanna keep it.
You can google "zipnadazilch" or "getrfree" for examples of freebie sites. I think anything4free is about the most popular freebie forum out there now that is free to join.
I made about 1500 bucks doing this a while back but its kind of a pain in the ass. I started out doing the trial offers and getting paid for being a referral. Then I started paying people to be referrals for me.
Doing the offers requires keeping up with all of the trials you do and canceling before the trial is up. Paying for referrals is easier cause you don't do any offers but you still have to coach the people on how to do the offers correctly to ensure they get credit.
The competition was getting pretty stiff back when I gave up on it and started doing other things but I'm not sure how it is now.