There isn't really a way to be 100% sure someone isn't cheating. Splicing, audio, visuals, hardware mods, scripting, etc. These things, depending on game, can be done with no way for the viewer to know if it's cheated or not. Most leaderboards operate on video proof and trust. If that video proof can't be determined to have been cheated, then it has to be taken as legitimate. The only way you can discredit legitimate looking proof is if the runner outs themselves as a cheater.

Having said that it still depends on the game/board. Some games even allow external hardware/software. I know years ago there was debate over using some adapter to make ESS easier in OoT. Something to do with joystick deadzones. Not sure what the outcome was, but the point is that hardware modification might not even be seen as cheating depending on the community.

[quote=Komrade]I know years ago there was debate over using some adapter to make ESS easier in OoT. Something to do with joystick deadzones. Not sure what the outcome was[/quote] Yes. the outcome for oot was to allow the use of the ess adapter fixing the disgusting wii vc deadzone to be similiar to the good old n64. however the majoras mask community decided to ban it

Ahh yeah that makes sense. It was the first thing I noticed when I played OoT on VC lmao. I guess there's a good example. Some will deem it cheating, others might not. Some communities will even allow turbo buttons even if turbo isn't standard to the system/base controllers.