And that is what I've done. I've also come here to note that hits are money; people coming here for no other purpose than to solicit traffic for their site are farming your site (us). As you said, currently that is allowed. My point is that the time to think about this and formulate a policy is before the spam becomes a problem.
Just as a prediction: we've had similar discussions about people posting their apps and such, and in each case, they kept at it until they did get smacked. Both posters have made second posts in a fairly short time and Example B has stated that he intends to keep doing so. It isn't going to be a question of if, but rather of when. They make more money by spamming more.
I would propose that there is a difference between a low post count poster who wants to link to something and a drive by who just wants to drum up business for his site. The latter group are not participating in your forums; they want your business to hang out on their site and read their ads. There isn't much difference between them and the folks who just want us to use their (Zygor) guide.
In Chinese: glasses are yanjing; eyes are yanjing, and the beer of Beijing is Yanjing. When speaking, the difference is in the tones. Did I just order a glass of beer or a glass of eyes?