Why buying links is bad
Web based SEO is based primarily upon organic reputation of a website. A websites reputation is based mostly upon the websites traffic, its feedback, how it is optimized, and by how many page links it has to other sites. Whereas the page links are suppose to be honest, some websites buy the links from other websites. This act of buying and selling links goes against Google and can impact the ranking of your website.
Little by little the various search engine are figuring out who is buying links and who is not. Search engines like Google are always coming up with new algorithms to help determine the credibility of the links. They are always encouraging people who know of any sites who participated in this to step forward and to help stop this growing problem.
If it is discovered that you have bought a link for your page you have a high chance of that link being banned by the search engine. Google does not tolerate these link sellers and they will go through great lengths to stop them from performing these sales. Remember, Google has money, brains, and a lot of incentive to stop this from happening, and they are always finding news ways to stop these acts.
Dont Buy Links
The reason why search engines are so against things like link selling is because they consider it a way to trick the search engine in order to get a higher ranking. Search engines love organic searches and they want everything to be placed in a certain place because they deserve to be there. If you buy a link you are cheating in a way, making it seem like you deserve to be higher than you actually are placing.
Honesty is always the best policy. If you are caught doing something like link buying or selling not only will Google ban the link, but they will also penalize your site for even trying to sneak into a higher score. If you keep honest you will maintain being on good terms with Google, and you can find the problems with your site and fix them instead of cheating to the top Google will be happy with your site and raise your stance accordingly.
Links that you had to buy for your site are not very beneficial to your site anyways. What would be the point of getting the link to a site that is irrelevant to your site and your product? One big point of getting links is to attract people from other websites to go directly to your site next. Linking means that this other site gives you credibility, but what is the point if you are link with some site that is random to what you do?
Dont Get Pulled In
Some sites may sell you empty links. This will make you look good from your website, but since the other end of the link is empty all that will happen is that users will click on it, find nothing there, and your credibility will go down. Another point to avoid link buying is that you will be getting no extra traffic to your site from the link. Getting traffic and credibility are the two main points to having links on your site, but buying links, especially empty links only hurt you in both aspects.
Some big websites do offer to sell you links to their site, but to buy a link that is to a real site can be very pricy. Websites who sell links know that the only reason you would buy the link is if you really want to get ahead in the rankings, so they will charge you quite a bit for that glory. For doing the transaction there is also a chance that it will hurt their the sellers site too, so that raises the price even more. Since there is a strong chance the link will hurt you in the end, why spend all that money for nothing?