Disguised spies are pesky, and frankly, a bit hard to find. Tips that will help to find them are; #1 If you run into a teammate and its like hitting a brick wall, (or feels glitchy), give 'em a good whack with your mele to test. if it damages them, use whatever you want 'cause its a spy ;D
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#2 If you see a scout or a medic going a bit slow, its a spy. (also, when being spy, when you are disguises as a certain class, you can go slower as a spy, but not faster)
-----------------------------------------------------------------------------------------------------------------------------#3 If you attack a disguised spy, and they die in 1 or 2 hits (depending on your weapon), go around the area shooting because its probably a Dead Ringer spy. These guys are pesky, because when you kill them, a clone/ragdoll is created, and the real spy can sneak away invisible. Also, dead ringer spie's clones are usually headless, or fall with their head folded under them.

Invisible spies, much like the disguised spies, are irritating, and quite stealthy (most of the time). Here are some tips on helping you find them:
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#1 Be sure to check a spy's favorite spot frequently; Corners and behind objects.
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#2 If you hear a fizzy/hissing sound, go around and give everyone you see a good whack. (also use rule 1 because the spy might have gone invis, too)
----------------------------------------------------------------------------------------------------------------------------- #3 Keep a close eye on chat; if a spy is disguised as you, they can use your voice. Someone's first response would be to tell everyone on your team, but DO NOT. They will tell others, and might forget to use team chat, and this will let the spy known you're onto him, so he'll change his disguise, thus letting the proscess start all over again.

Spy attacks can happen frequently on some servers, and might end badly if you dont try to spycheck. These are some tips on spy checking and trapping;
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#1 One of the most common ways to defend against spy attacks is using pyros to spycheck. This works most of the time, but not allways.
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#2 One of the ways I do it is setting up a decoy item, like a teleporter or dispencer, near my nest, but out of sight. This will attract the spies, and when they sap, you strike.

Thankyou for choosing my guide to help you in your fight against spies. If you like it or found it helpful, please Like and/or comment.