Deceptions and cons are a frequently occurring theme of Lost and an integral part of the drama and plotline of the show. Nearly every main character and many others have engaged in one, and many of the cons can be quite intricate and complex. Two of the show's main characters are themselves experts in this field; professional con man Sawyer, and expert manipulator Ben Linus.
Deceived her partners in the bank robbery about the goal of the robbery, then turned on them. ("Whatever the Case May Be")
Talked Sun into poisoning Jin in an attempt to get herself on the raft; additionally, deceived Sun into thinking she was nobly only trying to help her. ("Born to Run")
Helped Cassidy Phillips escape a jewelry con gone bad by saying her father ran a store and pretending to buy a "real" necklace. Later, she and Cassidy conceived a plan to evade the police so Kate could visit her mother. ("Left Behind")
Married Kevin under the false name Monica, then drugged him and left because of her shame at deceiving him. ("I Do")
Convinced Boone that her boyfriend Bryan was beating her so that Boone would pay off Bryan to leave her, and they could split the money. But her plan backfired when Bryan took the money and left. ("Hearts and Minds")
Re-established her connection to Boone, her stepbrother, by sleeping with him. ("Hearts and Minds")
They were shown wearing dirty clothes, later revealed to be costumes, such as when Eko and Jin saw them walk through the jungle; only seen from the leg down, their clothes appeared simplistic and raggedy.
They even used an entire decoy village that appeared very run-down; nothing like the highly modern Barracks that they actually lived in.
As a part of the plan, Jack would eventually be convinced to treat Ben's medical condition, a tumor on his spine.
Sent spies to infiltrate the Losties. ("A Tale of Two Cities")Ethan to infiltrate the mid-section Survivors, and Goodwin to infiltrate the Tailies. However, it appeared that he knowingly sent Goodwin on a mission he knew would be fatal because of his affection for his wife.
Attempted to manipulate Jack, Kate and Sawyer (during captivity) toward unknown ends.
Used Juliet's resemblance to Jack's ex-wife to manipulate him.
Pushed Kate and Sawyer into a situation where their emotions for each other would likely come out in the open.
Tricked Sawyer into believing they had implanted a pacemaker in his body that would cause his heart to explode if it started beating at a certain number per minute. ("Every Man for Himself")
Took part in Ben's plan to "break" Jack, using her own resemblance to his ex-wife Sarah.
Gave Jack a speech about the importance of saving Ben's life, while simultaneously playing him a video of herself holding cue cards asking Jack to play along but then kill Ben during the surgery. ("The Cost of Living")
Attempted to manipulate Kate into thinking they were "in it together" by handcuffing herself to her and putting her out in the jungle. ("One of Us")
Agreed to infiltrate the survivors for Ben and collect information on the pregnant women among them. ("One of Us")
One of the Man in Black's powers was his ability to impersonate the deceased perfectly, in terms of both appearance and voice. In general, this has granted him a great capacity to manipulate others and he almost certainly used it many times over his millennia spent on the island.
Throughout the fifth and six seasons, The Man in Black deceived everyone remaining on the island into thinking he was John Locke, all in a successful ploy to con Ben into killing Jacob by convincing Ben that Jacob was the cause of Ben's fall from grace. By the sixth season, it was figured out that he was an impostor. ("The Incident, Part 1")
Unable to kill Jacob's remaining candidates directly due to the Rules, The Man in Black fooled them into bringing a bomb onto Widmore's submarine (the survivors thought they were taking him surprise by trying to escape in it, but he knew they would). Jack had deduced that he wanted one of the survivors to attempt to defuse the bomb, which would in turn trigger it, thus being a loophole for the Man in Black's inability to kill them directly. An unconvinced Sawyer attempted to defuse the bomb, but this triggered it, resulting in the deaths of Sayid, Sun and Jin.
Although unconfirmed, it seems very likely that the entire The Pearl station was a deception. Its workers were led to believe that for the purposes of a psychological experiment, they were monitoring inhabitants of another DHARMA Initiative station, The Swan, who had been pushing the button on a computer. The people working at The Pearl would believe that the button had no purpose, and they were to monitor and log everything they observed at The Swan.
However, Desmond Hume postulated that perhaps the people stationed at The Pearl were the actual subjects of the experiment. This is not only substantiated by how pushing the button is indeed very important (as dangerous spikes in electromagnetism energy occur if the button isn't pressed, spikes that caused Oceanic Flight 815's crash), but also because of the enormous capsule dump consisting of pneumatic tubes sent out by those working at The Pearl; the size of the dump suggests that all of those reports were never read.
The pros of cons
The following are all, or have been, professional con artists: