In The Merchant of Venice, do people take advantage of each other?
Absolutely. Even "good" characters such as Portia take advantage of others, as her trick with her husband's ring shows. In fact, if we look at this play, it is possible to see it as one whole series of various characters taking advantage of each other for their own benefit or purposes. Let us just start by looking at some of the big examples. Of course, the most prominent example is how Bassanio takes advantage of Antonio's love for him to manipulate him and get more money out of him. In turn, Shylock exploits the weak position of Antonio and his financial vulnerability to make him agree to a deal that will place him in Shylock's power with the famous "pound of flesh" that will be forfeit.
Jessica is yet another character who exploits her father, not only eloping and becoming a Christian, but also stealing his wealth and wounding him with the sale of Shylock's wife's ring. The motives of the characters who supposedly marry for love are clearly suspect, as both Lorenzo and Bassanio are shown to gain wealth through those marriages, and thus it could be argued that they take advantage of their wives to enrich themselves. Lastly, Antonio, in the court scene, takes advantage of the power that he has over Shylock towards the end to impose a condition that is worse than death on his enemy. His insistence that Shylock converts to Christianity can be viewed as the final nail in Shylock's coffin of his living death. In fact, in a play that is so much about justice, it is somewhat ironic that so many characters take advantage of each other, but only one is punished for this.