Trading can work in destiny, just limit the trading system so that you can only trade one item at a time, both participants must have an item up for trade and it must be of equal value. Meaning exotic for exotic, legendary for legendary... It works and doesn't brake the game in anyway shape or form.
If you can find a flaw in my idea I'd be happy to hear it.
Edit: lock trading off until the level cap of 20 is reached
-
Or possibly limiting trading one item every week. This gives value to whatever you are trading so people won't be trading whenever they want. They must be selective on what they can trade because they only get one shot a week at it.