I'd advertise sites on here but I don't think the members would like me to do it lol but back to the main topic.
I'll just be covering TTG so heres what I do.
I look for a lobby post that says its free and join session. Just in case so you don't have to waste your time check the comments if theres any and his reputation and rank on TTG or whatever.
Now uhm lets say he's legit and free heres what you do
-type the hosts gt in a private chat and view his profile
-when it says joinable press B to back out of the view profile page
-and view his profile as fast as you can again
-"join session" should appear if you fast enough
-all you have to do is join session

Okay so if you can't get in then it's probably because the server is full it happens all the time just deal with it and keep trying.

You can use that method or you can just pay lol

NOW BUSTING SCAMMERS
Study how the jtag works, how you use keyvaults, and trick questions it's all I have to say lol