Firstly, how much does special forces/delta force do counter-intelligence stuff like blending in in urban environments? Secondly, I'm not military or intelligence, but I recommend Andy McNab's books (a former SAS operator that writes fiction starring himself as the protagonist)... it really gave me an insight into how this covert/spook stuff works. One of the most glaring issues is that when you're following a target or suspect in a city, you don't even let them SEE you, let alone make eye contact with them. Even an untrained individual could make a connection if he or see she's the same random guy twice, and then it's game over - no pun intended.