[rms]

A definition that errs on the side of marking spam sites as authorities is defining a spam site as one that exists solely for the purpose of selling links to other sites.

I would expect that these true spam sites exist as a link network somewhat seperate from the rest of the web. You could start manually defining filters based on what sites are actively selling links on the digital point forums.

We may have actually had this conversation in the real world, come to think of it.