I worked in auto finance -- and repossession for 8 years. Please be aware that companies are not obligated to work with the consolidation companies. Usually, the best the companies could accomplish would be things consumers could accomplish too if they knew how.
Most people don't call and ask for a lower rate, or focus on paying off your highest interest card first and paying the minimums on the others. In some cases they negiotiate "settlements" which can hit your credit. It other cases I've spoken to people that the settlement company was paying bills VERY late and the customer had no idea. Others may not know if you or your spouse became active duty military after you got the loan there is a "Soldiers and Sailors" act that protects you.
http://usmilitary.about.com/od/sscra/l/blsscra.htm
Some do more then that, but their success is largely dependant on the companies you have debt with. Plus... they don't do this for free. So when you're already tight on money giving a chunk to a company seems senseless.