KILL THE NINJAS!
It's happened to me and I'm sure alot of you on XBL... you setup a deal to trade a weapon, pet, or armor mod in Dungeon Defenders using the old trust system... you drop your item for exchange only to be kicked from the person's tavern you had an agreement with and that you trusted would be honorable. You've just been Ninja'd! And maybe you're pissed... rightfully so. But there's a chance you can get revenge (beside reporting to trendy in the report a player thread). It just involves simply dropping into their tavern with that same weapon equipped before you drop in, if you're lucky enough that they have that weapon they ninja'd from you equipped then the Ninja's item will be instantly deleted from their gamesave via the games on checks and balances (thank you Trendy!).
What you need to do is BACKUP your gamesaves and duplicate. I keep a gamesave on my harddrive and 2 usb duplicates.
Use Horizon or modio to extract your gamesave from a usb to your harddrive. Transfer the gamesave from the usb back to your harddrive. bring usb back to your computer and inject your gamesave back into the same usb. Now you have one backup. Now bring a SECOND usb to your xbox 360 and move your gamesave onto that. Bring that usb to your computer, use horizon or modio to extract the gamesave (again) to a different directory (I name dir something like USBstick2). Bring usb back to your xbox and put back on HDD, go back to your computer and inject that gamesave (don't mix the two!) and NOW you have TWO backups.
If you try to copy the SAME gamesave to two different USBs it will NOT work UNLESS you already know what the device ID is for that gamesave on that particular usb. When you try to load the gamesave from the usb it doesn't belong on the game will say that your game save is corrupt. I've listened to this happen to multiple people in my xbox parties ... they want to make sure they don't get ninja'd so they try to do a quick copy onto a 2nd usb and then loaded it, and freaked out because they lost all their stuff. Just do it properly and you'll be fine.
So now that I assume you'll have 1 to 2 backup copies, just quickly plug in your backup, load game save, equip the weapon that was stolen, wait for the ninja to start a different map (Yes, stalk them long enough in your recently played with players section, better yet, you should of had them send you an xbox message before you did the "trade" so you could keep track of them), if you're lucky enough that they're showing off/using that weapon then you'll have your revenge and their stolen weapon will disappear. YAY!!!!
Hope this helps some of you. :) Play nice and for your own sake in the long term, DON'T NINJA!