Hi Will,
Basically how it would work is if they sign-up from your free listing link (the one that ends with /go which is the one attached to the free listing e-card)
they will take 1 TCredit from you and give it to the new sign-up allowing them to place 1 free ad. If they try to place more ads, they would need to purchase more TCredits.
The important thing to remember when promoting the FREE listing is to have some TCredits in your own account... If you don't, SFI will give them a TCredit for you, but they will also TAKE one out of four of the customers who sign-up from your /go gateway. This only applies to the free listing, so when using it always have a few TCredits on hand in your own account.
Here's a reference:
http://www.sfimg.com/PopUp/TCFreeListing.jspThanks,
Tim