How is it that some seem to know the identity of a poster, or are they just guessing?

One way for example, let's say you were selling an item on totv, let's say a fertilizer spreader. If you included your phone number, one could Google the phone number.

1. Go to Find / Get someones IP Address
2. Scroll Down the page and fill the redirect URL with anything you want, for eg.Google
OR .Youtube
3. Now you have to use link for person. Go to Redirecting and shorten the link.
4. Now in any social engineering website chat windows send this link to your victim with a crafty message so that s/he desperately opens The link !!!
5. When you think he has opened the link use the link for yourself and open it in another tab.
6. In that website link you'll see the IP Address of the other poster.
How to use this tool ?
You can see on top of this page there are two generated links. The first link is for the person whose IP address you want to find. The second one is for you. First you need to copy the first link and send it to that person whose IP address you want. Then, using second link you can find the person's IP address if that person clicked on first link.

Thank you