I'm getting into mortgage lending, and we refer people who need to up their credit score to Veracity.
Basically, the legitimate services know the rules, and they will call up creditors who are in violation. For example, if there's a negative statement on your report, there are certain circumstances under which by law they must be removed, including a certain amount of time passing. But the creditors may not keep track of all that, so you can wind up showing a lower credit score than what it should be.
If you're worried about your credit rating, you need to be very careful which debts you pay off when, and you'll need somebody to advise you about that. For example, if you're about to purchase a home, and you've got a cell phone dispute dating back 5 years ago for 50 bucks, you're going to drop your credit score by paying the debt. Why? Because the biggest impact of financial activity is right after that activity occurs. What you've done by paying that bill now that you haven't paid for so long is to bring that back up to the surface so that it has just as much effect now as it did when the dispute first took place. That doesn't mean you shouldn't pay it, that just means you should buy the home first before your credit score takes a dive. Veracity can help you out with these tips and more though.
In your case, it sounds like a pretty sticky situation, and I don't know how you can get around filing for fraud and denying responsibility for the accounts. Unless you're just that nice of a person.
http://www.veracitycredit.com for details.