Does it mean Google CAN crack down other link selling sites, or link exchanging sites? If so, doesn't it affect link building method overall? SEO, I meant to include PPC also. If SEO is not working as it used to, what are the cause and what sort of SEO techniques you think are not working well? What SEO practice can get caught to be penalized? Buying links or link exchange? Seemingly safe link building practices (matching the relevancy) are OK or there is still a risk to be CAUGHT by Google?; thus there is always a risk anyway?