Yes, having been almost conned by XoftSpy into thinking my machine was rife with spyware, I would never trust an application that claims to find problems, then demands that you pay money for it to fix them. How do you know that the software itself hasn't 'planted' the issues it then claims to be able to repair, or is simply trying to scare you into a purchase by producing a list of false positives?
I would second Sam's recommendation of CCleaner, but make sure you create a back up of the Registry before removing anything, just in case.