Two questions:
1 - Would something like Double Hit disable focus sash? So if theres a focus sash Rampardos, and Ambipom does some kind of godly double hit, would it KO it or would it hang on with focus sash.
2 - If you see a Gyarados, and you have an obviously faster Thunderbolter or something, are you supposed to actually thunder bolt or suspect a switch to Electrivire/ground type/Jolteon?
It's really up to you. I'd use Thunderbolt for surprise (i.e. non-obvious Pokemon), or if you have a sturdy Electivire counter (Motor Drive just makes it faster, not more powerful). I personally have seen a lot of Gyarados, but only 1 Electivire, and that Electivire was on a team without Gyarados.