My favorite one-shot that I’ve ever ran involved the PCs being hired by a city to go kill some kobolds. The kobolds had taken over their mine, had fortified the place, and were violently rejecting any attempts to make them leave.

When the PCs arrive, it’s basically as described: The mine is overrun with kobolds, who have erected makeshift barricades and are armed with crossbows.

In actuality, the city had hired the kobolds to mine the ore for them, but then refused to pay them after taking delivery. It’s a labor dispute, and the PCs had been hired to kill them because nobody would question some adventurers killing some kobolds. The players discovered this and were upset enough about being lied to that they joined the kobolds’ side and basically acted as the (very well-armed and aggressive) union reps, negotiating better pay and more favorable terms for them. Was a great time.