Most injured workers are sincere, suffering and want to rapidly return to work. Obviously, there are those who are too impaired to return to work at this time or to the same job or able to ever return to work. Most are very honest about their limitations.
As to which symptoms or disorders are easiest to falsify, there are three:
At present, we have no definitive way to objectively identify any of these three. So when a patient states that they hurt, are depressed and/or are fearful of returning to their job, then we must assume that this is true.
Very often (but not always) the determination of their being disingenuous is made by looking at the nature of their presentation. Are their behaviors consistent with being in pain. That is do they exhibit pain behaviors or do they describe pain yet actually function with little or no limitations.
There are symptoms (called neurovegetative signs) of depression. A patient may say that he/she is depressed yet fail to have symptoms that would confirm that a depressive disorder is present. Stating that they are depressed is one of the ways in which patients can avoid returning to work.
Fear is most often expressed as though posttraumatic stress disorder exists. Complicating this is the overuse of that term to describe seemingly any emotional response after an injury (especially motor vehicle accidents). This is arguably the most difficult emotion to disprove. If the patient states that he/she is grossly fearful and cannot leave their residence, they can demonstrate that by merely staying home all day, every day, and watching television. Again, the only way to demonstrate that this is not accurate is to observe behavior which contradicts the claim of fear.