Link buying is a gray area. Google says buying links is bad, but there are some practices that skirt the edge of the subject, and the savvy webmaster may have questions regarding them.
An inbound link is a recommendation. We all want to gain a spot on the first page of the SERPs. If other sites link to us because they like our content, our product or our style, the are honest recommendations.
However, blatant attempt to skew the results by paying for links from other sources just to increase our ranking is looked upon very poorly. Companies which sell large amounts of links and advertise that they will substantially increase your Page Rank need to be looked at closely – the sites linked to you through such programs are often not relevant and cause you trouble. Most sites don’t need links from casinos and insurance sites; these send up a red flag to spiders that you are artificially trying to increase your PageRank by getting large numbers of incoming links that have little or no recommendations behind them.
Another common practice is to trade links, but reciprocal links are often not considered natural links … that said, if you are using your links mainly to get visitors to your site directly, then reciprocal links, links bought from websites relevant to your own and text links can be extremely beneficial. Just no-follow them so Google doesn’t think you are gaming the system. Play fair, don’t be evil, etc.
Social networking and blogging is the new link nirvana, and many blogs will offer to your site – for a price. This can gain you a ton of exposure, and bring traffic as well as links your way, but does this count as paid links? Better safe than sorry – if the blog links to you in the review, then by all means, no-follow it.
What about the readers who then check your site out and link to you independently?
Paying for a blog review is really just another form of advertising, in a way – not much different than paying for a keyword ad from Google. Natural linking as a result of a visit originating from either an ad or a blog should be treated equally.
With that in mind, keep your nose clean and no-follow links from paid reviews, but feel free to rake in the link love from readers!