There are a few ways to get "credits" without spending real money.
As you progress up in tiers, WGT gives you some (not much). When you get good enough to compete in tournaments, you can earn some credits (again, not much). Most of the CTTH (closest to the hole) tournaments are "random drawings" so it`s just a lottery of sorts to win credits.
The best way seems to be the "surveys" or other 3rd party offers that you can complete.
To find these, just click on "deposits and credits" under the FAQs------------->
Then click on the link "complete offers" that you`ll see on that page. Some people have gotten a Lot of credits (Free!) by doing this.