Paid links? shuts down used to be one of the popular link building services. The company has announced that it has shut down services because of a google de-indexing. This has happened to other service providers in the past. With this google sends a clear warning to all those people who are into paid link business, the message is clear you have to earn your links and not buy them. If you want to buy traffic then there is adwords.

This also means that website owners should take care of their link building efforts in-house, because its not safe to outsource the link building work to some other agency who might end up doing something that google doesnt like, esp these agencies are into paid links and google has specifically mentioned that its against paid links.
And websites who are selling paid links? I dont need to say anything more, you are on a path to be de-indexed.
On a daily basis, we monitor our domain network to check metrics like page rank, indexed pages, etc. As with any link-building network, some de-indexing activity is expected and ours has been within a permissible range for the past two years. Unfortunately, this morning, our scripts and manual checks have determined that the overwhelming majority of our network has been de-indexed (by Google), as of March 19, 2012. In our wildest dreams, there’s no way we could have imagined this happening. 
Read the post by the company here