Trust points: befriending a NPC?

Not sure this is the right place to post this, as it is both about game mechanics and about NPCs. Anyway... as I wrote a little "event" in the other shot I could not help thinking it would be nice if there could be "friendship/trust points" to be scored with some NPC characters by the hero in disguise that would open up new possibilities to open up for as alternative solutions to a puzzle.

Example: Very simply, if the hero is a regular soldier who met and fed SS Brandt's dogs 2 times, he could at a certain point be trusted to watch a door while Brandt goes to the toilet. On the other hand, if the player is an officer and/or keeps bumping into Brandt too often (even when offering meet), and/or never give anything, this could make the NPC "suspicious" (earn negative trust points) and make getting to the door more difficult...

Earning a pre-defined number of negative trust points with a NPC could cause the NPC to attack the hero even if this was in disguise... this number of points could be variable depending on the nature of the NPC (smarter/more suspicious) and the rank of the uniform the disguised hero is wearing (too high rank could be very suspicious rather than helpful, an engineer suit or lowly soldier uniform could make it easier to befriend soldiers and simple engineers, etc...)