Privateers

Privateer Ship

I'm interested in the history of privateers as well as their usefulness to the countries that employed them. I want to find out what made privateers so special. Why would any self respecting government approach a pirate and decide to hire them for their personal use, rather than spend that money on a bigger Navy? Does it have to do with the way privateers could get around the rules of war? Was hiring privateers cheaper than hiring new sailors that needed to be trained?
I've found several sources that examine these issues, and I intend to consult them when I research this topic. One source, cindyvallar.com, is an entire website devoted to examining key differences between pirates and privateers and the historical significance of privateers. I also found a blog written on the topic at marinermuseum.org. I hope these sources, as well as a few books I've been assigned in my English class, will help to offer insight to answer why privateers were so important to a nation's military.
Some problems I may encounter when researching this subject include a lack of information as well as historical inaccuracies. Many countries, I'm sure, tried to keep their use of privateers rather than their Navy as quiet as possible. This will likely cause a problem when trying to find specific pieces of information on the subject. Another problem is that countries only like to share their successful accomplishments, so there is the possibility of having history altered or embellished to make privateers look better.