If you are after a comprehensive book that outlines qualitative research I would highly recommend this. Detailed postgraduate level, although very understandable. Interesting case studies from many disciplines. The one I found most memorable was a study searching through people’s rubbish and this found that in America poorer people buy branded smaller packets whereas richer people buy non-branded larger packets.
Survive Like a Spy: Real CIA Operatives Reveal How They Stay Safe in a Dangerous World and How You Can Too by Jason Hanson
Starts off about how to recruit spies – if trying to recruiting someone who indicates he feels insecure about his career, they will likely tell