Fan Works / Rewarded As A Traitor Deserves

In Amazing Fantasy, it's revealed in the last legs of "The Enforcers!" that information about Nighteye's raid on Mysterio's warehouse was leaked by a corrupt police chief Mysterio had bribed, leading to the operation's complete and utter failure. The chief is later found riddled with bullet holes atop a car after being dropped from a hundred feet in the air by Vulture.
My Hero Academia: Unchained Predator: Abraham's reward for betraying David Shield is getting burned alive by Volcano.
In Buffy the Vampire Slayer/Supergirl crossover The Vampire of Steel, a vampire mook slays his abusive mob boss and then tries to cut a deal with Buffy and Supergirl, claiming that he did "their work for them". Buffy stakes him.

Wikibending: The Southern Water Tribe traitors who sold information about Katara's waterbending to the Fire Nation were executed by being dropped down an icy crevasse.

A Brighter Dark: Before leaving for negotiations, Garon orders Corrin to conquer one of the provinces that seceded from Hoshido in order to send a message to all.

Divided and Entwined: The muggleborn Beckett turns a fellow muggleborn in to the Aurors, leading to them recieving the Dementor's Kiss. The Resistance repays his betrayal by blowing up his shop while he's inside.

A Thing of Vikings: Mildew dies without a weapon in his hand and while fleeing from a battlefield (in this case, an erupting volcano), which disqualifies him from ever entering Valhalla. And his employer Mac Bethad, who he had defected to, was planning to off him anyway once he was no longer useful.

Ages of Shadow features a minor example — after the Himinate conquers a small kingdom only because the king's brother betrays him, the Shadow Walkers repay him by placing him right behind the king on the Human Sacrifice menu.
Queen of Shadows: During the Shadowkhan's conquest of Kyushu, several samurai betray their lord, in order to earn favor with their new masters. Ikazuki is so disgusted with this, that he has all the offenders gelded, cuts out their tongues, and has written explanations of their treachery carved into their flesh, before sending them off to toil as slave laborers until they die.

For His Own Sake: In the climax, Kagura betrays Chisato by throwing them at the police in order to distract from their own escape. Just when they think they're in the clear, they realize to their horror that Mayako, the sister of one of her previous victims, is driving her limo. She then drives straight off a cliff.

Aftermath of a Fallen Star: Shining Armor and the Royal Guard take the time to torture Blueblood before his execution, simply to drive home their contempt for his betrayal.
In The Elements of Friendship Book I: Harmony, Madam Oleander sells out Harthind and the Mane Six to NightMare Moon, in exchange for the restoration of her youth. Instead, NightMare Moon kills her.
The Nuptialverse: Metamorphosis reveals that Chrysalis was once a pegasus, but betrayed her own kind in order to gain power from Discord. He transformed her into a hideous changeling, treating her as his slave and making her live in fear of suffering a Fate Worse than Death if she ever betrays him.
Pony POV Series: When Chrysalis was a nameless genetic deviant, she lived as a prisoner with other genetically deviant changelings, including one known as #1992-PT. On one occasion, the deviants made a plan to escape, but #1992-PT secretly informed the guards about it, who promised they wouldn’t tell the deviants it had been her. As soon as the escape attempt was foiled, the guards told the deviants exactly who had informed on them, and then threw #1992-PT back in their cell. Chrysalis never reveals what the deviants did to her in retribution, only that it was rather nasty.

in dreams you follow (but I dream in the dark): When Kiba needs to murder a high-profile target in order to sell his Fake Defector ploy, he chooses Danzo due to his involvement in making Shino's cousin Torune disappear. Tsunade signs off on this due to Danzo's defiance of her authority and attempts to undermine her.
Senju Of Wave: Danzo is killed after appearing to murder the Kyuubi's jinchuuriki.
Whirlpools Among The Eddies: Kabuto and the Sound Four make clear that if Karin is caught betraying Sound, she'll be subjected to a Fate Worse than Death.

Averted in Black Out The Sky; Despite their Fantastic Racism, the White Fang accepts the aid of any humans who join their cause, treating them as equal to the Faunus among their number.

Chasing Dragons: When Drogo lays siege to Qohor, with the priests of the Black Goat preparing to invoke their god against him by mass sacrificing the children of the city's magisters, the magister in charge of the Unsullied offers to open the gates and let the Dothraki in, in exchange for his household being spared. Drogo agrees, the city is sacked, and said magister and his family are executed via trampling by the horde because even Dothraki look down on that kind of treachery, even if it helps them. Besides, Drogo promised that no Dothraki would hurt the magister's family, but made no promises about their horses.
In The King Nobody Wanted, Selyse Florent betrays their house to the Dragon court, exposing their conspiracy and slandering them with claims that they were conducting Human Sacrifices. Exact Words is then employed against them so that they don't get the reward they desired — they were promised a great marriage, and get sent to the Faith, married to the Gods themselves.

In XCOM: The Hades Contingency, the Council of Nations strikes a deal with Zhang, offering him asylum in exchange for the alien artifact in his possession. However, they order the Commander to surrender Zhang to them for trial, with execution or life imprisonment the most likely outcomes. The Commander proceeds to defy the trope by offering Zhang a position at XCOM, though he offers an olive branch to the Council by letting them send people to interrogate him about the Triads.

Rewarded As A Traitor Deserves / Fan Works