If you are about to complete a quest, perform the following tasks to gain unlimited EXP + GOLD (exclude auto-saved Boss fights):
1) save the process through checkpoint or use option "save and quit" in the Start menu
2) reload the game and complete the quest w/o Saving until you grab your Reward + EXP
3) Go to Start menu, then Options, set your file saving preference to soft-save (note: Soft-Save save only stats + inventory, not the quest process), then save the game now.
4) Quit the game, simply hit the Power button
5) Turn on the device and reload the saved process, and you should find yourself still in the middle of the quest you have left (step 1) but with the EXP + Reward from completed the quest (step 3)
This trick doesn't work on auto-saved Boss battles, but it works fine on a manually saved battles, you can still get a chance to loot some rare/epic gear drops.