Hi, making this thread to help you secure a Minecraft account.
I recommend using @Zyger for all Minecraft deals as he is the best at securing accounts and if you're unexperienced it is probably the safest option.
Once you've purchased your account go to hotmail.com or outlook.com or live.com, sign in to the account. You may need a code from the seller.
Once you've signed in click on the top right corner. After that click on "My Microsoft Account". Once your there, go to Devices. Its the last one at the top in the blue. If there are any devices remove them. To remove them click on "View Details" there should be an option to remove them on the right hand side. Click out of it and go to a different page and click back to see if its actually removed.
In the blue background, where you originally were when you pressed "My Microsoft account" go to "Security", after that go to "Advanced Security options" (you may need another code from the seller) and then remove the ones the current person has. You have to have at least one email added. I recommend also adding an google authenticator app for two step verification. To do that scroll down to "Two-step verification" -> "Turn-on" -> "Next" "set up a different Authenticator app." -> then save the key it gives you in a text file, use the same text file for the rest of the account info. You will need to go to https://zyger.net/middleman/2fa/ and enter the key to get the code. You will need this every time you login or you can receive a code to your email that you linked. Regularly check https://account.live.com/Activity to see if the seller is actively trying to take the account back while your doing this.
Scroll down to very bottom of the current page and click "Generate a new code". Save the code it gives you in the same file as the key, you are able to reobtain access using this code. Above this also press the "Sign me out" button so it signs all other devices out. Next scroll back all the way up to Enter password, you're going to change the password. Save the new one in the same text file as all the other things you have so far. Make sure this is a complex password, just spam your keyboard.
In the top left of the screen, click on "Your info". Change all the Microsoft info like the DOB, Full name, and Country. Here, or below the Account info section on the current page click on Sign in preferences. Change the alias, you can add an existing one or make a new one. You can only do this twice a week, and 10 times a year. This may be the most important step. After that make your alias the primary one and MAKE sure to remove the old one and any others like phone number etc.
Make the seller screenshare and have them log out of https://minecraft.net/, https://account.microsoft.com/, the Minecraft launcher. Make sure to check Emails & accounts on windows, as that could be a sneaky way to keep the account logged in. You may also have them check Lunar client and badlion although they should be logged out of those when you change the info.
Make sure the exploit is not on your account. Head to https://zyger.net/middleman/exploit/ and copy paste the email. If the exploit isn't being used this is good. If it is you'll have to message @Zyger to get it removed ASAP as the account is vulnerable to getting recovered.
If I missed anything let me know.