I found on my e-mail Saturday is the day to shop at GameStop. I assume this works online too.
GameStop Elite Pro is $30 a year to get 30 points per dollar or $0.03 towards in store rewards certificate, 20% off pre-owned games
GameStop Pro is $15 a year to get 20 points per dollar or $0.02 towards in store rewards certificate, 10% off pre-owned games
GameStop standard is Free to get 10 points per dollar or $0.01 towards in store rewards certificate
Trading in games gets you an extra 10% credit for everyone.
During this Saturday it is double points for everyone for what you buy so I suggest you start getting some gift cards. I get discounted GameStop cards to get PSN credit/Xbone/Lyft/Uber/Sling/Steam because those work with store credits and GameStop gift cards. $100 PSN credit on the Pro Elite $30 a year program for example would get you $6 back in rewards where normally you get $3.