In a recent Google+ hangout, Google’s John Mueller said that a website can lose its trust from Google so that it does not pass PageRank value anymore:
“With regards to PageRank, I think the main issues that we see there are really if we recognize that this is a site that it doesn’t make any sense to pass any PageRank from. Then, on a site level, we might say, okay, we’re not going to pass any PageRank from here.
That can happen, for example, if we can tell this is a site where people have been spamming their links for a long time, and it’s maybe an open forum where all the links are followed, and it’s filled with clutter.
So those are the kind of situations where we say, well, we see this site is having trouble, maybe they can’t keep up, maybe they’re doing this on purpose. And we just don’t want to trust it with regards to our PageRank calculations.”
You can view the video here: