I am the one who tagged both of the above users as spam. tacocat's explanation describes exactly why I did so. There are other users who mostly post links to one website, but with only one exception, I haven't marked any of those posts as spam.
When I'm bored, I go to global feed and mark things as spam. Here's my rationale:
1. If a user has commented, or shared posts from any other user, I do not mark their posts as spam.
2. If a user comments on their own posts when someone responds, I also don't mark their posts as spam.
3. If a user has self-promoted several posts in a row that have no shares or comments, I mark their posts as spam. If someone continuously posts things that no one in this community has interest in, it's spam.
4. If someone posts a new post every day, from the same website, then they're posting far more than most other people in the community. This is a good indicator, but not a guarantee, of spam. Most quality posts are not released on a daily basis, because good writing takes longer to read than it does to write.
I have no real problem with self-promotion. A fair amount of our regular uses do it. But I do have a problem with users who are not at all otherwise engaged with the community self-promoting. I have a rather low toleration for "blogspam" as it's commonly called on reddit, and I don't like people using online communities that they are not members of as an advertising platform. I don't think I'm alone in thinking this.
If 6d6rpg and rangergames want to comment on this, I'd be glad to hear their opinions. Assuming they are people, and not bots. If most people would prefer me to block these users rather than mark them as spam, I'll do so, but I marked those posts as spam assuming that most hubskians did not want to see those posts, either. As klein mentioned, if you follow #rpg and block #spam, you should still see those posts, so Devac, I know I'm not inconveniencing you directly.
Also, I'd like to point out that hubski does not work like reddit. #rpg isn't a subreddit, and the content posted with that tag isn't only visible to people who follow that tag. As such, it isn't like reddit, where I can safely ignore posts that don't interest me by not subscribing to #rpg. I would have to block #rpg, which I don't want to do, because several posts using that tag do interest me, just not those posted in excess by a few users. Any post, no matter the tags shows up to everyone who doesn't filter them. It's how Hubski is designed. This is a very small site, so the design works well.