That's not hax; if a 100% flinch chance doesn't happen, that Pokemon has Inner Focus or used something that out-prioritized Fake Out (meaning that they flinched, but after they did something so it was irrelevant)
EDIT: Or, apparently, Hariyama's Sheer Force got rid of the flinch chance. Good to know
Generation (pi)(i). When you see this, raise e to the generation and add 1. Social experiment.
Because Fake Out has +3 priority and Sheer Force Fake Out could possibly be the best revenge-kill move ever (besides Ambipom Technician Fake Out, since STAB 60 BP Fake Out), since not even Extremespeed or Feint have that high of priority.
IIRC the trainers in battle facilities have set movesets but random abilities. Hence why you occasionally see things holding Flame/Toxic Orbs without abusing Guts etc. - they rolled a different ability for that battle.