Both are safe instruments. The cashier's check is paid by the bank's account, not the person who purchases it. It is very safe and very negotiable. It is also more difficult to place a stop payment on a cashier's check than a money order, so in that sense, the former will be paid easier and faster than a money order. It also depends on where you get the money order. A money order from the Post Office is usually very sound.
Either of these can be faked by a thief. You do have to trust the person you are dealing with if you receive one, and don't spend the money from either until you are absolutely sure the funds are in your account, and the item you deposited has cleared the bank from which it is drawn.
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