If you go back 5 years, everyone was using Quake 3 Arena as the benchmark. ATI got in some hot water because if you renamed quake3.exe to quack3.exe, your FPS would drop by 15%, because they were silently reducing quality to juice their benchmark numbers.
Apparently people did this with the DirectX "3D Tunnel" demo as well[1] back over 20 years ago.
Also there was one "that checked if you were printing a specific string used by a popular benchmark program. If so, then it only drew the string a quarter of the time and merely returned without doing anything the other three quarters of the time".