Since you can’t see who is watching, you should take control of what they can see. If you are worried about prying eyes, adjust your privacy settings:
A: No. Any paid service is a scam. Facebook’s API explicitly prohibits fetching profile viewer data. facebook profile viewer
While you can’t see who just browsed your page silently, Facebook does provide legitimate tools to see who is interacting with you: Since you can’t see who is watching, you
The Facebook Profile Viewer is a useful tool that allows users to view Facebook profiles in a more organized and accessible way. Here's a potential development of this tool: facebook profile viewer
Tap and follow the on-screen prompts to provide feedback. Reporting Without an Account