In his opus magnum, The Scarlet Letter, Nathaniel Hawthorne wrote,
No man, for any considerable period, can wear one face to himself, and another to the multitude, without finally getting bewildered as to which may be the true.
For several of the deceptive characters of Shakespeare's play Hamlet this statement is, indeed, true, and because of its truth, the deception of certain characters becomes so damaging to them and to others.
Perhaps the most egregious use of deception is in the character of Polonius. Even his speech is a facade. For instance, he tells King Claudius that
...brevity is the soul of wit,
And tediousness the limbs and outward flourishes (2.2.90-91)
Yet. he is highly verbose himself. Added to this fault, he is extremely deceptive, even to his children, Laertes and Ophelia. delivering to his son in Act I, Scene 3 a long diatribe against being dishonorable when he himelf epitomizes deceit and corruption as he has Reynaldo follow Laertes and even impugn his reputations to serve as probes to the truth of Laertes actions; he manipulates the king and queen and hides behind the arras to evesdrop on Hamlet and his mother. Further, Polonius exploits his daughter by instructing her to not spend time or even talk to Hamlet so that Hamlet will be further disturbed. Then, Polonius will have the proof he wants to prove that Hamlet is mad, but, in so doing, he blocks the love of Ophelia and Hamlet for each other,and, thus, effects poor Ophelia's madness and death.
Tragically for him, too, the false face and the deception of Polonius become his nemesis as in his corruption and desire for political position, he effects his own death. by violating his own platitudes.
His criminal deception comes to haunt Claudius as he fears that Hamlet will have him killed. Consequently, he sends Rosencrantz and Guildenstern to spy upon Hamlet, and later to take him purportedly to England, where he will be assassinated. But, when Hamlet has the players re-enact the murderous actions of Claudius, the king becomes nervous and even remorseful in Act III, scene 3. Nevertheless, he continues to plot against Hamlet and enlists Laertes in his nefarious plot to have Hamlet slain. At no time is the deception of Claudiius honorable or justified as it is always designed to serve his own desires without concern for others.
Instructed by her father Polonius to cease contact with Hamlet and return his love letters, Ophelia finds herself victimized in her false face as Hamlet deals her only cruel words and taunts.
While Hamlet pays a high price for his playing mad with Ophelia, his duplicity with Guildenstern and Rosencrantz does save his life as he foils their plot to have him killed in England. His clever manipulation of the play by the actors, disturbs Claudius and thereby convinces Hamlet of his uncle's guilt which, in turn, effects his actions in Act V that free the Danish court of its corruption.
I think that this is a fascinating question. I would like to add to its complexity in suggesting that perhaps the deception that makes the drama of the characters even more intense is that some of them engage in self- deception. For example, Hamlet is torn between his own ends of action and inaction, of function and surmise. He is so driven internally by different polarities of thought that he deceives himself in recognizing that he knows "the answer" or "the path." In order for a person to effectively deceive another, they have to be concealing something that they know they are going to act upon and keep this hidden from others. This becomes the basis of deception. I don't think that Hamlet is a character who fully grasps or ascertains what he exactly wants. His deception of others might be fed because he himself is deceived about his own ends and what he needs to do in order to achieve them. It is here where deception takes on a whole new and complex level, making him one of the most intricate characters in literature. This makes it difficult to ascertain justification because Hamlet is so layered in self deception that the deception offered to other characters is a secondary issue. The only absolute we know is that this challenge in understanding of self precludes any meaningful relationship from forming, except with that of a spirit and a corpse. It is here where one might be able to say that deception of both other and self might not be able to be seen as justified if it precludes a healthy and effective communication with another.