Since
kdpierre cited one of my comments as the inspiration for this thread, I guess I should respond

Though I had to go back and locate my actual post, because I couldn't remember what I'd said to inspire this thread.
Basically, many of the spankings I describe in my stories are completely unreasonable and unrealistic, some going well beyond 1000 spanks. I'm no "spanking virgin", though it has been quite a long time since I've had the opportunity to spank anybody. In fact, I've only had one spanking partner, and she was a genuine "virgin" in all senses of the word when we first began our relationship. As far as I recall, she wasn't spanked as a child; the first spanking she ever got came from me.
Despite her "inexperience", she turned out to have an astonishing (to me, at the time) level of pain tolerance. But, despite that tolerance, the longest spanking I ever gave her amounted to approximately 200 spanks. And that was with a light wooden ruler, and the majority of the spanks weren't especially hard. They just stung quite a bit. It was the only spanking I ever gave her that resulted in tears. She was 19 years old at the time.
Yet, in my stories, wherein most of my spankees are aged 14-17, hard spankings with paddles and belts frequently get into "hundreds" territory. My own personal experience tells me that spankings like that are completely unrealistic for girls in that age range. Yet I still write them.
To put it bluntly, I look at spanking fiction, or any other form of erotic fiction, in the same way that I look at Hollywood action movies. What are the most important factors in an action movie (or any other kind of movie)? Characterization (are the characters, and their motivations realistic?) and Story (is the plot sensible and believable?). As long as the answer to those two questions are "Yes", then the "action" is just frosting on the cake. Is the "action" in an "action movie" believable? In most cases the answer is "Absolutely not!". The action is, more often than not, completely over the top, and completely ridiculous. Like a car chase that results in millions of dollars in property damage. How often does that really happen in real life? The answer is probably "never".
As long as the Characters are believable and relatable, and the Story is believable and makes sense, then I expect most of us are able to suspend our disbelief when it comes to the Action.
So it is the same in spanking fiction, or any other genre of erotic fiction. Is a 500-stroke paddling any less believable than a series of vanilla sex scenes wherein every male character is swinging a 10" penis, and every female character sports massive breasts? In my opinion, "no". "Believability", to me, is not important when it comes to the "action" in a story.