Google's John Mueller said that not all links are given full weight and does not pass the full signals it can potentially pass. Instead, Google might not pass any weight from the link or might pass partial weight from the link.
John said this on this past Friday's video hangout at the 1:23 minute mark where he said "we don't give every link that we find full weight."
Here is the transcript:
I think the question is, how does Google recognize paid links? From our point of view, we take a lot of different things into account, we don't give every link that we find full weight.So even if we are not sure, something can be somewhere in between. But it is a number of things we take into account there. It is not just if someone reported it as a paid link because random people on the internet report a lot of things that aren't necessarily true. But at the same time sometimes there is useful information.
So there are a lot of things that come together with regards to paid links.
Here is the video embed:
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