The reason I'm not citing anything is because there's nothing to cite. The (mis)representation in this case is crystal clear: "I want to fly to city B."
How does buying something indicate your intent, wants, or wishes? If I buy a can of spray-paint, the store has no idea if I am using it to paint my child's bicycle, tag graffiti, use it as a weapon and hit someone on the head, or as part of a wonderful "Rube Goldberg" device which at the end an implement hits the sprayhead which sprays through a bright white light as part of performance art.
Another example, a true story: yesterday I visited an ice cream store with my friend. She wanted a scoop with chocolate sauce, and I wanted just a scoop. 1 scoop was 4.29+tax. A 3 scoop sundae with chocolate, nuts, and strawberry-sauce was 7.98+tax. Even though we only wanted 2 scoops we got the sundae because it was cheaper and scooped the strawberry-sauce off and into the trash (crazy I know, we don't like it). Did we defraud the ice cream store?
People buy "more than they need" all the time, and purchasing a good provides no intent as to what one wants or how they wish to use it.
Because when you buy a united ticket you agree to a contract of carriage that specifically says you will use the ticket in its entirety.
And what makes it most ridiculous is this: "Any practice that United believes, in its sole discretion, is exploitative, abusive or that manipulates/bypasses/overrides United’s fare and ticket rules."
Can they ban me from United- yes. Can they try to collect money and threaten me with a credit dent? They can, until they ran into a lawyer or into a motivated person with time and resources on their hands.
Apart from proving that you intentionally bought a return flight best of luck defining this as fraud in front of a judge.
I booked two flights to Paris for my girlfriend and me. Before we left she found out that she has to return a day ealier. Instead of rebooking the flight (which would have been insanely expensive) she chose to return by train.
Arriving at the airport for the return segment I proceeded to the gate and informed the airline employee that my girlfriend will not make the flight and that I would like to check her out.
Instead of busting me and denying boarding (which would be the logical conclusion of your asessment) she thanked me profusely and I went on my merry ways (waiting for and eventually boarding the flight).
Now, you can certainly argue that we didn't know about her earlier return when booking the ticket. But we sure knew about it when boarding for the first segment. Nevertheless and despite the tickets running under the same record locator I did not have any problems boarding the return flight nor was I approached by the airline later.
Of course it could be that European airlines are generally not as hard nosed as United (they generally also don't rough up their passengers, but I digress). But I think it's more to the point that it's impossible to prove that I never intended to take the return flight. It certainly would be more obvious for hidden city / nested bookings strategies that I intended to save money (I would be very reluctant to call that fraud).
Moreover, fraud is a criminal concept. Violating the contract of carriage is certainly not.
But the language of a contract of adhesion doesn't seem likely to be taken as a representation by the non-drafting party in a fraud case.