I rarely record video because it takes up so much disk space, and Elite's performance nosedived catastrophically after Beyond was launched, but I've encountered three (ever) situations where I didn't know for certain that someone was cheating, but suspected as much.
1
Corvette vs FdL; I was interdicted in my PVE boat and their FdL started shooting immediately with a weird loadout of frags and MC. I'm an adequate pilot at best and so figured I was in for a pretty even fight vs an experienced PVPer, despite my enormous shield and sustained DPS advantage. Anyway, after about 30 seconds I realised I was clearly the better pilot and could just plink away at his prismatics. Now I KNOW you can engineer some pretty ridiculous prismatics on an FdL but I had excellent ToT with this FdL and expected with two C4 MCs and a bunch of beams to be doing at least SOME damage to him. I had a single C1 FC railgun ready for his bank but it never happened. I probably consumed 1250 MC ammo per C4 hardpoint, the vast majority of which hit his shields, and whilst the outer ring faded a little, I would estimate he was still at 75% shields after around 5 mins of sustained fire. As tempting as it was to kill a rubbish ganker who thought he'd 'have a go' I didn't have the time or the ammo to keep engaging them.
2
A gank squad of three interdicted me after a long-ish journey back from Quince or Sothis (I forget which) to Jameson in my 70+LY DBX taxi. I high waked ASAP because the taxi isn't armed, and can't boost more than twice without a nice long rest, but I figured I was safe because I'd picked something too far away from Shinrarta to be followed. Anyway, I was just browsing the right panel in SC to check the damage taken and some of the same gank squad appeared again - FdL and iCutter. Now, we're talking 20-30 seconds since I finished the jump - so less than 90 seconds for sure since they would have been informed of my 'surge detected' hi-wake charging. Now, a stripped-down, lightly-armed iCutter with a 5H guardian premium jumponium could probably manage 65LY in a single hop, so the 20-30 seconds would be believable since that's all it would take to wake-scan, charge and jump after me. The FdL, jumping 65LY in a single hop?
No way.
60LY at best with god-roll legacy mods, guardian booster and premium jumponium used as well.
3
The most recent one was earlier this year in a PVE wing for a BH community goal. I winged up with a random CMDR in the instance and he was being lightly harassed by an iCourier that posed no real threat to him. I lumbered within range to thump the shields off it with with two LR C4 fixed beams and it ran away on half hull only to come back with an couple of FdL friends a few minutes later. I'm guessing my Corvette had about 50-60% shields (~6000MJ effective, so maybe ~3000MJ left) at the time they started firing and I wasn't dumb enough to try and fight a wing of three PVP gankers who had a headstart in an all-beam PVE laserbarge. At least one of them had phasing sequence but I always run with at least an MRP and a couple of HRPs to avoid the sudden death of a paper-thin hull if I do something stupid and lose shields. Off the top of my head, the effective armour against thermal is ~3500MJ) Phasing is 10% penetration I think, so at 50% shields I was expecting the shields taking at least 90% of the damage to give out long before the undamaged hull. Anyway, my modules started malfunctioning immediately (I assumed grom missiles and drag munitions) but I was surprised to see the cockpit go dark and 'eject, eject, eject' when my shields hadn't dropped yet. To this day I have no idea how they did that - perhaps there was a gank fleet of 10+ ships with long-range rails and they all fired simultaneously for an insta-kill, or perhaps there was some kind of super-laggy wing of torpedo boats that had somehow managed to get the 6 torps necessary to take down my generator and also then landed another 3500MJ of hull damage all in the space of one lagspike.
So no, I can't be sure I've seen someone cheating, but even knowing how ridiculous some of the engineering can be in this game, those three situations all defy likely explanations that aren't "cheaters using a hack"
FDL's can't have over 30,000 MJ shields.
FDL's can't jump 65LY in a single hop
Phasing sequence lasers can't do 3500 MJ of hull damage without taking out just 3000 MJ of shields.
So there's three examples where I was extremely suspicious of cheating, but potentially I've been attacked by cheaters and not realised on many more occasions; either dying and assuming I was lacking combat skill and situational judgement, or simply running away to lick my wounded pride.