I think you have to define "unfair."

In my favorite stories, the heroine is often punished for capricious, silly, or "unfair" reasons, at least on the face of it. Indeed, is there ever really a "just" reason to spank an adult woman? No. But thematically, the heroine is punished not because of her misdeed, but because of her "naughty" desire to be spanked.
In THE TALK by Chard T. Shelly is punished by her mother after her mom discovers the family's computer is littered with the history of her daughter's visits to spanking story sites (like our library, no doubt!) Shelly confesses to her mom that she has always wanted to know what a spanking was like, and her mom points out that leaving the history there for her little brother to find COULD be considered a spank-able offense. Shelly is spanked for a "crime", yes, but she is really spanked because of her curiosity.
In KAT'S CURIOSITY by TipTopper the heroine goes to the Principal to ask for a spanking...she gets it, and then some, when the Principal discovers that she is not wearing regulation panties.
In BRITTANY'S WARM RETURN TO KENTWOOD HIGH by EdB a famous Pop-tart borrows her friends school uniform to returns to High School and experience an old fashioned spanking. Her crime? Talking in the class she never attended, an offense that results in a painful bare bottom spanking and a humiliating session of corner time.
In DJ Black's BACK TO SCHOOL the schoolmaster's wife puts on her old school uniform and sneaks back into school for the express purpose of getting a spanking. Unfortunately, when an investor arrives with her husband's boss, her punishment becomes painfully realistic. To her shock and horror, she also ends up enrolled in the school for the rest of the semester, where the investor will expect to see her regularly disciplined.
The last point is key. In all these cases, the good girl's WANT to be punished, but once the punishment process starts, they behave and feel like any other naughty girl who desperately wants to avoid the first (or next) spank! They're all Butterflys in their tummies, sweaty palms, tears, and promises to be "good."
Of course they haven't really been bad? Or have they? Is the desire to be spanked itself a spankable offense? In these stories it certainly is. And what more appropriate punishment for a good girl with naughty fantasies than to experience the punishment she gloated over when others got it?
In all these stories too the punishment is more severe, painful, and realistic than the girl had imagined. The punishment for her fantasy is the painful reality of bare bottom discipline.
In THE MAGISTRATE Goodgulf makes this case in a very clever way. The Magistrate's goody-goody niece, Tracy, visits the prison to see her Uncle. But when her naughty curiosity about spanking gets the best of her and she decides to wait to see her Uncle in the same room where the female prisoners are waiting to be punished she is mistaken for an inmate. By the time her Uncle arrives Tracy is stripped, gagged, and tied down over the whipping bench, and as her bottom looks as naughty as the other four inmates her Uncle announces the punishments are to commences forthwith.
"Grunts and squeals arose from the waiting 'culprits about to be on the receiving end of justice', but they were ignored. "
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Goodgulf uses the grammar to lump Tracy in with the "other miscreants" about to receive "justice" -- thus stating what the reader already feels in their heart: Good girl Tracy is in fact a very naughty girl, and her punishment is as just as if she had tried to blow up parliament.
Unjust punishments? Perhaps. But inside every good girl reading this post now is a naughty girl just asking to be spanked.