During the age of sail warships would sometimes pretend to be civilian vessels to lure privateers in. When the privateers closed in the warship would run up it's colors, their national flag, and open fire at point-blank.

There's a standard method for an infantry unit retreating from an ambush - Instead of running straight away from the ambush you retreat at an angle from the ambush. Troops leapfrog past each other, firing back at the ambushing for. Since they're moving at an agle it sounds like more soldiers are joining the fight from the flank. The purpose is to deceive the ambushing forces in to thinking you've got more soldiers than you do so they don't pursue you.

There's a famous story from the Romance of the Three Kingdoms. Zhuge Liang is famous for being the smartest sonoremovedun in China. He routinely pulled off brilliant strategic and tactical victories, achieving stunning results effortlessly. Well, one time, he was supposed to defend a city, but his army was still two or three days away, marching hard to catch up with him. An enemy army was approaching the city and Zhuge Liang had basically no forces to defend with.

This absolute fucking madman opens the gates, then sits out from calmly playing guitar. When the enemy general gets word that Zhuge Liang is sitting outside with the gates wide open having a jam session he says "Okay fuck this. I don't want to deal with Zhuge Liang's bullshit today. let's go attack somewhere else" and they leave.

More than one prisoner has escaped prison using fake guns carved out of soap or whatever they had handy. Lots of people have used a finger, or a piece of pipe, or whatever to convince a bank teller they have a gun when they don't.

Cold Reading is a classic tactic in most cons and in interogations where you pretend to know more than you do, using carefully worded questions to convince the person you're interogating that you already know what's up, to convince them to talk about what's up, when you really don't know what's up.