from: http://www.tf2tactics.com/entry.php?32-Understanding-Spy-Sentry-Kills
As a spy there are so many skills that you have to master in order to be an effective sentry killer. The following is a list of these:
STAB & SAP: The most common and the most sure fire way of taking out a sentry. You stab the engineer and quickly sap the sentry before it starts firing on you. Circle strafing helps tremendously.
SAP & STAB: Commonly used if other sentries are nearby. You sap first and quickly stab the engineer. Players new to the spy class might think this tactic is a good way to start practicing killing a sentry. I actually found it harder...
SAP, SAP & SAP: The beginner's way of destroying a sentry. But thic tactic is quite effective against a cluster of buildings. As it creates a lot of confusion, and eventually the engineer won't be able to keep up.
TELE-FRAG & SAP: This was recently discovered and proved to be very effective against engineers bundled together in a confined spot--making a conventional sneak attack harder to pull off.
TELE, STAB & SAP: Can be used when the engineer is already aware of the tele-frag trick. Instead of sapping his entrance, just use it normally--he won't expect you popping up behind him!
OVER STAB & SAP: This is typically employed against engineers who stay and camp their sentry with their backs against a wall. You first get on top, decloak, crouch and stab.
LURE KILL, DISGUISE & SAP: Lure the engineer away from his sentry gun, usually by sapping one of his buildings. Sap, cloak, and wait for the engineer to come and repair it. Then uncloak, stab and sap his sentry.
CAMP KILL & SAP: This is done by camping on his dispenser until the time is right. Usually when you hear an uber incoming, that would be a good time.
AMBASSADOR KILL: This is done by going to the back or side of the sentry, while being out of range. Headshot the engineer to kill him, then you are free to shoot his sentry.
DIVIDE AND CONQUER: This should be done if you are having a hard time doing your job as a spy. Players clustered together with sentries isn't a very ideal place for a spy to sneak into. So kill their teleports and make them spread apart.
STALK, STAB & SAP: Wait for the engineer to leave the safety of his sentry, then stab him when you can. This is useful against engineers who never stand still.
KILL ENGINEER WITH SENTRY: This isn't really very practical, but there are very few situations when this tactic will be doable.
http://www.tf2tactics.com/
6:10 best idea of killing ever!
jumboman232 2 weeks ago 7
I liked the part when he sapped the sentry
PiggyPigOfPorkines 1 week ago 5