Simple rule of thumb.
"If you have to ask......"
Simple answer too - you have a friend that is willing to do YOU (and you only) OCCASIONAL favors. Simple as that. now you're not being a fukstick for not telling them, its simply a problem that your source is limited and not open for business with other people. Add in something about being paranoid too if need be
That line or random variations of it can apply to CC and NC sources alike.
Generally if someone is a decent friend, I'll offer to pick it up for them... but they're still not getting my source. Source only goes to people that I REALLY know.