Years ago, I got my credit reports via snail mail and noticed that there were some glaring errors. There were 2 addresses that I never lived at, a bank account that wasn't mine, credit card that wasn't mine, and some other minor inaccuracies.
How did this happen? Some moron had just stolen my identity and tried to order 6 desktop PC's from Dell and Gateway. Yes, six! Like two or three weren't enough. Jerk.
Fortunately, Gateway called me (I was a customer at the time) and asked if I had placed this order. I said heck no. They stopped the order and communicated with Dell not to ship theirs either. However, I was stuck with a number of detrimental items on my credit reports that I had to prove weren't mine and have them removed. No doubt they were also dropping my credit scores like a rock.
I even had to fill out a police report at my local station too to make it official (and send to the credit reporting agencies).
So does all this stuff affect credit scores?
To answer your first question, YES. If you've got inaccurate information on your credit reports, your credit scores will be negatively affected. If you fix or "repair" your credit reports, your credit score will go up.
Now, not everyone will have been victim of identity theft. Some people are late on their bills, forget to pay off something, or have other bad stuff on their credit reports. These too will all affect your credit scores.
Now, to your second question.
I'm a do-it-myself type of guy, so I handled it all on my own. But, many people simply don't have the time nor the patience and prefer someone to do it for them. It's not necessary, but may be more convenient.
Raise your credit score (do-it-yourself) and solve your problem, click here.
Pay someone to do it for you, click here.
As well, below are some great ideas, tips and suggestions to help you get started.