A solution would also be, gold trading or depositing forbidden for the first 7 days (assuming 7 is the amount of days it takes for blizzard to detect and ban fraud accounts). Yeah, it kind of disables legit player chance to use the AH, but they can always use them in other chars. If Blizzard is not doing your solution, or mine,or anything that the gazillion of superbly payed developers they have can come up with in seconds, is simply because they don't want to. And if they don't want to, is because they are profiting from the situation. How are they profiting is another story, we might never know.
Tinfoil hat mode engaged. I say insurance claims/fraud and or increase false sales projection so the shareholders are satisfied. Tinfoil hat + tinfoil router mode engaged. (A) blizzard employee(s) are involved in the level 90 fraud, just like someone from blizzard was involved with the dupes back in the d2 days.