Google's Spam Filter

"I suppose when Google does testing of different fine-tunings of its organic results, similar to a spam filter, it’s often a balance between letting too much spam in the top results, or throwing out too many relevant sites. Is that true? What are your thoughts on this? Sure, I could stop all the spam in the world if I didn’t have to return any search results. :) Usually we try for changes that are across the board wins in terms of relevance/topicality and spam. There’s a large class of good sites that are pretty easy to recognize as good sites. But it’s true that there can be a balance between topical sites that are spammy and high-quality sites that are less on-topic." Source: blog.outer-court.com