Is rapport a cognitive phenomenon? "Building rapport" is often mentioned as one of the most fundamental sales techniques, but I had a hard time understanding the cognitive mechanism behind this. Is this really a state of awareness that can be analysed via cognitive science tools, or just a salespeople buzzword?
"Building rapport" is not actually A technique, but a general phrase that may cover a whole lot of specific techniques.

"Rapport" does not normally occur in scientific contexts, it mostly occurs within anecdotal subjects like sales and NLP.
Individual sales techniques and NLP is usually not based on science at all, so they do not care for what is scientifically correct or what can be scientifically studied.
"Rapport" consists of several smaller subjects, like trust, various psychological phenomenons, various unconscious processes, emotions, etc etc etc - which are the common phenomenons to refer to in science.
So "rapport" is nothing more than an umbrella term including several phenomenons that are far from restricted to "rapport".
Thus it would not even make sense to study "rapport" specifically.

Also note that sales techniques and NLP tutors like to give their own names on phenomenons and processes that already have a scientific name for them.
I noticed this as I read a book on NLP by Richard Bandler, and this may be another reason why "rapport" has not made its way into science. 

The field of "rapport" was never meant to be based on science, and you are not meant to look those things up in science.
This means two things:


Don't expect what you learn about "rapport" to make any sense scientifically, because it's not based on science at all.
If you want to better understand that which is actually supported by science, then you need to search for a more specific phenomenon.