You're 'under no' (legal) 'obligation' to return the money. [=there is no law that requires you to return the money; you do not have to return the money]
The firm must fulfill its 'obligations' under the contract. = The firm must fulfill its contractual 'obligations'.
You can try the machine for free 'without obligation'. [=without being required to buy it or to do anything else]
(..) Argumentative. You're damn right it's argumentative. Because he knows that laws have been broken, and he has an obligation to report it. Miss Leeds... But if this is the way you want to play it, the Attorney General has given me a broad mandate to uncover what went on. (..)2011 TvShow: Suits Title: Rules of the Game Season: 1 Episode 11