You don't quite have it right. "Ra" stands for "Rare" and "Ex" stands for "Exclusive." The meanings are relatively clear if you think about what those words mean.
You can only have one of any Rare item. (They're rare, after all.)
You can't give/sell/trade an Exclusive item to another player. (They are exclusive to you.)
Rare/Exclusive is just the combination of those two: You can only have one, and only you can have it.
There are separate flags for whether items can be put on the AH, in bazaar, sold to merchants, etc. But those flags aren't visible on the item; you just have to find out by trying, or by looking it up.
Edit: Here, have a couple links.
Ex and
Ra.