Apples or oranges?
On the contrary, it appears that there is a need to screen the workers as they leave the secured area.
The travelers are those being served by TSA, while the staffers are subject to whatever legally permissible conditions their employer wishes to impose. If exit screening of the TSA employees is made a job requirement, there is nothing the workforce can do to stop it.
A very simple approach would be to adopt the real-world practice of limiting what employees are allowed to bring into a secured area. The TSA folks are neither flight crew nor techs, so they should need to bring nothing with them beyond their lunch, their ID and their personal keys, all of which could be secured in the non-sterile area. Obviously, an employee cannot leave the secured area carrying an item he was not permitted to bring in.
In this case, it is evident that the employee involved was not the sharpest knife in the drawer, since Ebay is not a particularly discreet venue in which to offer hot, easily identified merchandise. It makes you wonder how widespread the problem is. It seems perfectly reasonable to insist that TSA more closely monitor its own staff.