I think the real problem is that there is no way to tell if an item has been purchased or not.
Status ostracization for those folks who just pop on, lay down a grand for top gear so they can "roll noobs in pvp" would be fine.
The problem is that there is no realistic non-circumventable way of tagging items as purchased over found, while still maintaining an open trade system.
EDIT: Just occurred to me... A way of inspecting a persons account and viewing their recent purchases might work, except that they could always just do so on a different account and then trade it to themselves. Maybe if purchased items were locked to their purchased account, permanently or for a certain number of days, or if only accounts with high level characters could purchase auction house items... or some combination.