Yes. I have. I have a low credit score that I am working my BUTT off to fix. I get at least a couple of these offers each week. I throw them all away. In the fine print terms of these so-called "helpers" it explains they are going to charge you $29 for this, $99 for that, $49 fee, etc.
Throw them all away.
To help your credit, it is best to find a bank (credit unions are good) that will give you a secured credit card. In these instances, you put up the money. For ex., if you give them $300 to hold, they will give you a credit card for $300. It works like a Simon gift card (gift VISA) only a secured CC is reported to the bureaus... so by making timely payments on it, you build a good credit history. Just don't max it out... try to stay under 50% of your limit. Often times, after a year or so of successful payments, the bank will give you an unsecured credit card.