What deliberate attempts are made at deception in Hamlet?
One of the most outstanding examples of purposeful deception is the one that Hamlet perpetrates on Claudius when he decides that he ought to be sure that Claudius thinks him mad. He tells his mother to inform the new king that she is worried for Hamlet's sanity and that he really appears to be mad so that Claudius will not discover the plans that Hamlet is making to find out whether he did in fact murder Hamlet Sr.
Obviously the other is the counter-strike planned by Claudius to send Hamlet to England with Rosencrantz and Guildenstern and have him killed along the way. He has the two friends pretend to be in Denmark to visit with Hamlet and that he has some errand to run for the king in England while all the while plotting with the pirates to have Hamlet killed and dumped over the side.
You also have deception practiced readily at the end of the play with all the poison and intrigue of the final scenes.