Fraud

There is fraud when, through the insidious (crafty, deceptive, tricky) words or machinations of one of the contracting parties, the other is induced to enter into a contract which, without them, he would not have agreed to. 

Undue Influence

There is undue influence when a person takes improper advantage of his power over the will of another, depriving the latter of a reasonable freedom of choice. The following circumstances shall be considered: the confidential, family, spiritual and other relations between the parties, or the fact that the person alleged to have been unduly influenced was suffering from mental weakness, or was ignorant or in financial distress. – Heirs of William Sevilla and Leopoldo Sevilla