Avoid Being Penalized

Even if a site like that has decent link popularity you can usually bet that they will be losing it soon if they exchange links with all kinds of random sites. Link exchange works up until a point and then eventually it become link farm. A link farm is a site with a bunch of completely unrelated links scattered about in no logical order.

Eventually overly aggressive sites get penalized, but webmasters using those techniques will usually have already started another site, and you may end up suffering for their greed if you link exchange with incredibly aggressive sites.

Another trick they may use is to have you link into their good site and have them link to you from a different domain of essentially no value. Since their good site is not going to get penalized (because it does not link out to anyone) it does not matter much to them if their bad site and your site receive a spam penalty for being part of a link farm.

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