Yeah just be cautious, whatever company you're thinking of please type it in this sites search bar because you'll see real people who have encountered these places and what their experiences are. also the BBB is a great resource as well and don't be afraid to type it into google either. though you will probably get biased search results if the company pays the money to market, you should still see reviews and such on whatever company you're thinking of.
That aside, I have to agree that if you can do it yourself please try to do that because no one takes care of you better than you and you know you're doing things right. see what steps you can take to better your credit on your own, may take some time but that's ok...trust me in time your scores will go up if you actively pursue getting it done