One reason fighting paid links is so difficult

I contacted a website today with a pointer to a great new article that I just published. The writer that wrote the article probably spent more than 20 hours on it. I spent another 10-15 hours, and the editor that worked on it spend 3-5. It's a 1600+ word article that nails an important commercial topic, and it's a very strong piece of work.

As part of promoting the article, I contacted a number of websites that are interested in the vertical that this article covers. One of the replies that I received said:

"We normally charge $25 to include links, but I've waived it in this case and added a link to the article to XYZ.com"

Has Google flagged XYZ.com in the past for selling links?

In my opinion, this link should pass PageRank. I think Google should think that it should pass PageRank. Yet there's simply no way (unless they're parsing Gmail messages with some very sophisticated algorithms) that they could attain a sophisticated enough understanding of my site's relationship with XYZ.com to correctly pass PageRank on this post, but not the ones that are sold for $25.

The reality is that there's a chance that this link will pass PageRank (ie Google hasn't penalized them for selling links in the past). Or, as I understand how Google addresses paid links, the link simply won't hurt me. I suppose the net takeaway is that I'm glad I don't have Google's job!