[sdossick]

It is functionally trivial to rotate IPs from the "test phones". There are shady brokers who will sell you Residential IP-based proxy servers (hacked home machines which will proxy your calls and make them appear to come from homes all around the world).

[z3t4]

I mean in an audit, the test person can install the app on a device he/she has physical access to. And conclude that his/her phone was registered on the ad agency logs, yet no ad where shown. The fraudsters could however make it so the phone only sends fake impressions after a certain amount of engagement, so that audit/test person would have to play "my little pony" eg the child game - for one week ...