Jobs that require clearance can be like this. You'll be amazed at the questions they asked, really invasive ones. (Not about me, about my friend). It's commonplace and I've done it before. I can't say the job here, that should give you an idea.
Advice can. Be destructive to a friendship, I've seen it happen, and so it's something I try not to give. That's not to say I don't, but one must pick the mark and situation carefully I think. That quote you wrote says it all perfectly.