As for preventing people from hacking, having serverside checks after the fact is fine (so if you really weren't physically able to do something, it'd basically retroactively put you back where you were and deal damage to you accordingly, kinda like GGPO resets, but on an individual level.) but games like WoW also had GMs watching top-tier fights live (and invisibly) to check for shenanigans, as one possible example of how things are done.