I am having a horrible time trying to figure out how to join the Thieves Guild. I can't seem to do it.

Somewhere I read if you have that "Unusual Gem", you can take it to "The Ratway" in Riftin, and see Vex in "The Ragged Flagon", and from there it will all start.
Or at least Vex will recognize you have the "Unusual Gem" in your inventory, and she will send you on some gem finding mission.

Well, I happen to have the "Unusual Gem". So I went to see Vex. I even met that guy "Maul" that told me to take the Gem to Vex.
So I have found the whole Ragged Flagon place, and see Vex, and she wont converse with me.

So this is a 2 part issue. Not only can I not seem to join the Thieves Guild. But I can not get this Unusual Gem thing started.

Any help would be appreciated -

Thanks !

There is a guy in the town center of Riften, near all the shop stalls, that will give you a quest to enter the guild

Ahh, ok, is that the guy that asks me to reverse pickpocket some stolen items into that jewelers pocket so he can get him arrested ?

Yes

Sweet, yea I seen him a while ago, but denied the job because it seemed fuct to do to somebody.

So if I am understanding this correctly, doing this job causes two things to happen.

1- Makes Vex talk to me, in turn allows her to recognize the Gem in my inventory and start the whole gem stone retrieving mission
and
2 - Starts up the motions to allow me to join the Thieves Guild

And in reverse, to further clarify this, not doing that job will NOT allow you to achieve either of the above ?