Agree the warnings. From time to time, I download one of those "free check-up" programmes for a laugh. They usually end with a message something like "We found 857 problems on your PC. We'll tell you about the first 50 and leave you to try to work out how to fix them. If you want us to fix them, or to tell you about the other 807, send $49.99 or fill in your credit card details..."
The 50 they find are usually cookies and the like, which I could have deleted with a few mouse-clicks in Firefox.
There's also a "driver finder" that gets shoved at you from all directions. It doesn't find drivers, it just asks for money. Win 7 and manufacturers' websites found me all the drivers I need.
Anything that reckons it will "tune up" your PC will usually end up deleting operating system files or parts of your installed software. Been there, done that, not going there any more.