One of the key preconditions for an exchange to be euvoluntary is "no regret." That is, the buyer must actually get something like what (s)he expects, and must actually want it.
A story about a law suit, called to our attention by alert reader Benjamin C., goes like this:
A Michigan resident is suing FilmDistrict because their newly released film "Drive" was not enough like "The Fast and The Furious." From the class-action lawsuit, the plaintiff hopes both to get back the $10 she spent on her movie ticket and to legally put "an end to misleading movie trailers." The article, which can be accessed here, asks whether "the advertising has been so deceiving as to be illegal."
Benjamin asks whether "we might also consider whether or not government has any business saying that a movie about driving can't be advertised with footage of a man driving."
Or, more technically, even if we agree that the exchange is not euvoluntary, the state should still allow the transaction. The young woman wanted to see a kind of "The Fast and the Furious" remixed, and actually thought that is what she was buying a ticket for. But the harm of regret has to be balanced against the harm of preventing advertising a movie about driving using (as Benjamin notes) "footage of a man driving."
UPDATE: Patrick at PopeHat has a nice analysis, and more background.