There are all sorts of ways to find things out, which I'm not going to list here for what are, I hope, obvious reasons. I've used various free tools to discover who was trolling my website: it was easy, and took only a few moments. And it's even easier if the person whose true identity you're after doesn't know about these things and doesn't understand how they work.
That you have to ask implies to me that you're in that category. Which means you're also not going to know what you should do to protect your true identity if you do decide to go ahead with this.
Although this sort of derails my own thread, I'll take the bait and respond to this properly.
Here's how I think you catch those who troll your Website. You link the IP address they use to post a message on your site to the IP address they use when they post on this forum. You use some type of tracker or analytic software on your Website to obtain their IP address there and your Moderator status allows you to see the IP address of every forum member on this site when they post a comment.
If you really want to get into cyberstalker mode, you could then do a search on the email address they used to register an account here to see if they've used it elsewhere. You can also do a search on their username. Many people usually use the same email account and/or username on multiple different sites such as twitter, facebook, instagram...etc.
Then, if you really, really want to go into creepy cyberstalker mode, you will cyberstalk their facebook, twitter & instagram friends. Sooner or later (usually sooner) you'll find a friend who displays all of their pictures to the public. You'll probably find a picture of the "troll" as well.
This is just the tip of the iceberg. You can use this information listed above to find their linkedin profile and possibly even their work contact # on various other Websites. The list goes on and on. So, I do have a pretty good idea of how this works.
Now for the good part. This is what I'd do to prevent this from happening. I'd create a new email account to register with Amazon. I'd use a pen name that I haven't used anywhere else in the past. And the most important part, if I wanted complete anonymity, I wouldn't tell anyone that I self published an ebook.
This way there are no links. So, for example, if I were to visit your Website and leave a rude comment (I wouldn't do that
) you would certainly link it to my username here and know it was me, unless I used a VPN, proxy or TOR to post the comment on your Website.
So now you know that I am the culprit. If you decided to get even by leaving a negative review of my book you would then attempt to uncover my pen name but you would run into a brick wall since none of the information I used on Amazon matches the information I used here. Even the name docmarty and the email account I used to register this account would lead nowhere.
Obviously, nothing is foolproof. However, there are ways to remain anonymous online as Alice pointed out earlier. While it's true that I'm not familiar with pen names as this is all new to me, I refuse to accept that remaining anonymous is not possible. If you can prove me wrong, please do. It would be educational for a lot of people.