Commission and fee are what Gameflip takes from your sell price. Suppose you sell a gift card code for $100, there’s a 8% commission and 2% digital fee so you get $90 total (100 - 100*(0.08+0.02)).
All subscriptions have a 0% digital fee. Gamer Club subscription has 0% commission but you can sell up to $50 worth of items. Pro Club has a 6% commission but you can sell up to $500 worth of items.