@Edent
If I got the video in binary form, I could read enough of the #ffmpeg man page to adjust the brightness and contrast myself. The results wouldn't be as good as a specialist could produce, certainly, but they'd be enough to tell me whether the enhanced video could plausibly have been derived from the original.
For non-geeks, my answer is quite different: we can't be sure of any evidence presented in court, because witnesses, police officers and experts could be lying. That's why we have perjury laws with such stiff penalties. If you can't get your hands on the evidence yourself, you ultimately have to trust the system.