Exchange 101 for Dummies (or Noobs)
Don't use the Exchange to transfer items between your characters. I see a lot of Noobs (I assume) posting valuable items for 1 or 100 ce, thinking that they will just logout and back in on their other toon and purchase it. Wrong! Someone else will snatch it up first.
Anything that could be sold on the Exchange could be mailed instead. Just enter your handle and send it to yourself.
You can use the Exchange to transfer money between your characters. Post something cheap (like a tribble) for the amount that you want to tranfer. Try to pick an amount that will be easy to located when you do a search. Log out and then log in with your character with the cash. Purchase the item and you should almost immediately get an email that your item sold. Log out and then back in to your original character and he should have the money. Example: To transfer 1 mil from Doc Lee (rich) to Jho'dig (poor), Jho'dig posts a tribble on the exchange for 1 mil then logs out. Doc Lee logs in and purchases the item, then logs out. Jho'dig logs in and has 1 mil credits.
You can also use the Exchange system as temp storage. I'm sure that Cryptic did not intend for players to use it that way but it works. When you see an item posted on the Exchange for 999,999,999 credits, someone is banking it. They've set the price so high that they know that nobody will touch it. The system isn't foolproof as I've had a couple items I was saving get purchased. Yes, it is stupid for them to buy my items when cheaper items are available but it happens. I can only assume that they thought my item was more valuable since it had a really high price tag.
Hope this helps. :-)