Being unable to cancel your trade at the risk of getting the slot disabled is absolutely insane and is the reason I'm quitting before I get to experience the full game.
You won't suffer the penalty if the trade falls under one of these conditions: 1. It has been less than 5 minutes of posting the trade. 2. It's been more than 4 hours since posting the trade. 3. One of the items has sold from the posted trade. 4. It's an upgraded trading slot. We hope this helps.
Quite glitchy. For a while at level 60 all the blobs were bouncing around so crazily that I couldn't see anything until finally the screen just glitched and there was nothing. http://i.imgur.com/rgmhPtO.png
 "NGU IDLE"){kind=icon}
 "We Become What We Behold"){kind=icon}
 "Shop Heroes"){kind=icon}
 "A Small Favor"){kind=icon}
 "Bit Heroes"){kind=icon}
 "Papa Louie: When Pizzas Attack! - Kongregate Version"){kind=icon}
 "Crusaders of the Lost Idols"){kind=icon}
 "Feed the King"){kind=icon}
 "Omigario : Agario with bullets and sprint!"){kind=icon}
 "The Splitting"){kind=icon}
 "Starlight Xmas"){kind=icon}
 "Dawn of the Dragons"){kind=icon}
 "Coloruid"){kind=icon}
 "Papa's Pizzeria"){kind=icon}
 "Check Flag"){kind=icon}
 "Sentry Knight Conquest"){kind=icon}
 "Cube Escape: Harvey's Box"){kind=icon}
 "Kana Warrior / かなウォリアー"){kind=icon}
You won't suffer the penalty if the trade falls under one of these conditions: 1. It has been less than 5 minutes of posting the trade. 2. It's been more than 4 hours since posting the trade. 3. One of the items has sold from the posted trade. 4. It's an upgraded trading slot. We hope this helps.