>It's a reflexion of the person that does it, not of the receiver end.

My response is also to your point. This takes a long time to learn, but it is the best superpower anyone has against (for the sake of argument) "manipulative people" (including PDs and non PDs) 

But I do also believe Occam's razor presents itself again. I don't think most people (especially adults) that aren't in romantic relationships (or courtship and the like) intend to manipulate the other.

I simply think most people are just "lazy". I know I can be. Lazy to respond because what you said may not have been a high priority for them. Keyword PRIORITY. If it takes energy, especially though, you'll get left on read. It's not malice intent. So your job as the initiator is to know this and make them adjust their priorities (tell them you want an answer), or let it go.  

To beat this as a "lazy" person from my example above, is to just do something about it asap. If someone sends you a message or phone call, immediately rank it's priority, then respond in a reasonable time, with SOME answer. My experience in customer service has been exactly this. Tell them something, even if it's not what they want to hear. It just conveys to the other person you did in fact take the time to care to them personally, even for a moment. And lets them know where you stand on that priority list.