In the case of Charles, Alice, and Charlie's $100 situation, when it comes to restitution, which requires that a person return what that person has unfairly gained. This is a situation an unjust enrichment event in which a person (Bob) should return a benefit conferred if the benefit was not conferred as a gift and was not conferred officiously, that is, against the person's wishes (Bix, 2012).

Furthermore, in the situation with Megabank, it was the banks fault for erroneously paying out the wrong accounts. Alice does have a claim or burden of proof that she should be compensated for her $100 loss. With that said, the bank has an obligation to recover the money sent to Bob. The return of money paid by mistake is a classic case where the appropriate remedy is restitution.

Finally, when Alice sold her painting for a discounted price, unbeknownst to her, she sold it for less than market value. It doesn't matter the fact of her selling the painting to Charlie or her brother. What comes into play is that Charlie knew he could make a profit and sold it to Bob before having to return the painting for a slightly higher price. In this case this situation could fall under "quantum valebant", when the plaintiff gets a money judgment for the fair market value of goods that the defendant received from plaintiff or restitution where there is not a contract. Since Alice conferred a benefit on Charlie and since she accidently sold the painting to him which could lead to it being unjust to allow him to retain the benefit, she could be entitled to the reasonable value of the benefit conferred.