I have seen a lot of buyers out there have no idea what they are doing so I will give you a bit of advice that will save your site down the road.
Do not buy from sellers that are too open about where they sell there links. 
The following are red flags that indicate link sellers you should stay clear of:

• Posting their URL in a forum
• Send you via a PM or Email a listing of all their publisher sites before they know who you are.
  • Rest assured, if they are sending you a list of their URLs, many other people are getting the same list and it will eventually be forwared to the wrong people.
• Sellers that sell massize amounts of links on a single page to anyone who will buy.
• Seller with "networks" of sites.  Networks create foot prints.  Anyone can look at the backlinks of one buyer on the network to find all the other sites in the network.  Don't think the search engines don't know this.

The above should be a good start. 
GooGooGuy