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]
(..) Why should I help you? Because my vermin is a former student of yours. And considering the student, I'd say you have a rather large obligation. You can sleep here. It will take me a month... ...to make the sword. I suggest you spend it practicing. I've completed doing... (..)2003 Kill Bill: Vol. 1