None unusual. lying is a very important and constructive evolved tool; it is only considered bad as part of the current system of control. People lie for a reason, it is a requirement for survival. That is why we are very good at it. What makes a good lie? Mostly truth and only fabricate the parts required. Stick to stuff you know and are comfortable with. A double agent would be troubled by deception unless they were psychopathic. They would start to care for the people they were infiltrating.
Having some experience at being someone I was not, while working for a law firm that handled insurance fraud and messy divorces, I assume there are some shared personality flaws with those who ply the much shadier business of spy craft. First and foremost, you must have a gift for sizing people up, be able to compartmentalize your life to the extent that you can turn the real you on and off with a switch, and when you show up for work, leave your ethics and morals at the door. When done properly, the mark will have not the slightest notion you've intruded into their life. The goal is to have them invite you into their circle, and just let them talk. Most crooks are insanely stupid, you need only give them an audience.
