How does Google discover a link farm? When I purchase links, I should make sure that the links are not from link farm, right? But how do I know if it's a link farm? Thanks!
Any page even if it is on a super authoritative site could be turned into a link farm if: 1- Has hundred of external links (make sense why one page has to have 300 external links) 2- Text to link ratio is very high (count the number of clickable words and divide it by the number of none clickable words the higher it goes the worst) 3- No relevancy, you see links to casinos, health, cars, sport on the same page Lots of link seller on DP turned their blogs almost to a link farm by selling more than hundred links to different niches in their blogroll, in this situation even if it is not a link farm I do not know what pagerank will be left for these sites. So may be what you need to worry about is getting links from pages with low number of inbound link, do not worry much about defining it as a link farm or not