Alternate exploit
Utilizing the save method, you can effectively farm cash and items through item duplication. Drop the item on the ground you want duplicated from your map reference save and then import your character. Pick up the item and you now have 2, update your map reference save and then drop both items now. Import your character and pick up both items and you now have 4 of this item. This growth is exponential and over time will amount to insane amounts of cash if your selling, or you can duplicate your favorite weapon to dual wield, or just duplicate augmentations to slot into your armor.

NOTE: on the alternate exploit it is only necessary to have 1 save spot available.

Secrets
Quick attacks
If you have a one handed weapon equiped press the block button and attack button simultaneously to do a very quck strike, use this on a close enemy and you can see the damage rank up.

Glitches
Save exploit
Make sure you have room on your memory card for more than one save. The idea behind the cheat is to import your own character into a map you control. So, if you are after experience fight your way through the game to a boss fight with an easily accessible save point. Fight the boss down to the last hit and then withdraw to the save point. Save the game, this will be the map reference. Now, go ahead and wander back towards the boss and kill him. You gain the xp and loot of the boss fight. Return to the save point and save your game on < Create New Save Game >. This will create a new save that we'll use to import from. Now, exit the game and reload your map reference save (1st save). Once inside your game, hit start and go to Add/Remove Players... Highlight your own character and hit triangle to import a character. Import your character that already has the boss experience into the map reference save you created and you now have the opportunity to kill the boss again (in one blow no less) and regain his xp and loot.

The only cheat for this game
This cheat allows your character to unlock 75,000 coins, 999 skill points, and level 20. it is during gameplay, press and hold L1 + R2 + Triangle + R3.