I have a simple solution to the GTN scamming problem Bioware. Allow users to set purchase thresholds. If the user wants to buy something in excess of their threshold, they are given a prompt asking if they really want to do this and type yes if they really do.
So for example I set a threshold at 100K, and wish to buy the Mask of Revan for 8 million credits. The prompt comes up, "This purchase exceeds your spending threshold, do you wish to proceed?". I type yes in the provided text box and the purchase goes through. If on the other hand, the midlithe crystal I am trying to purchase for 6K actually turns out to be 6 million (as happened to me today) I have a chance to realize my mistake.
I can't tell you how frustrating this is. And yes trolls, I know it's my own fault for not being careful enough, but it is none the less extremely frustrating and far too easy to do unless one is careful never to let their guard down. I would counter that the GTN should not have to be that stressful. I am sure you have lost players/subscribers to this problem, having briefly considered moving on to another game myself after experiencing the frustration of watching a month worth of savings destroyed in a minute to a scammer.
My problem aside, the solution I am suggesting would be very helpful, would require little effort to implement, and help Bioware maintain subscribers. I hope you will give it careful consideration.