Why should you pay somebody to help you fix your credit, when it’s obvious that most of their results are often temporary at best? Handling your problems will teach you financial discipline and make you a better judge of finance going forward in life.
When you use the service of credit repair companies to fix your bad credit, you will be forced to share your personal information with them before they can do anything about your credit situation. I would not want to share this information with them, and neither should you.
The truth is that you can do exactly what these companies do, if you learn how to do it. Most "credit repair companies" write letters to credit bureaus, listing few pieces of information that are false on your credit report. When the credit bureau gets the information from a credit repair company, they will then start investigating it.
Since you have the legal right to obtain (and dispute) a copy of your credit report, you can improve your credit score much more effectively on your own.