Let's suppose the novel begins like this: "The client's name was Aloysius Archibald Wilberforce Smith, and my job was to shadow his ex-wife, Mehitabel Arabella Jones, hoping to determine whether George could justify writing her back into his will. Mehitabel was a dashing young woman and, even though she had abandoned Aloysius for reasons he still didn't understand, he still loved her."
At one time such names as Mehitabel, Arabella, and Aloysius, Archibald, Wilberforce were in common use. They have all become rare, for whatever reason. Our hypothetical novelist--let's call him Mike, because what the hell, it's a popular name--can call his detective's quarry Mehitabel Arabella Jones if he wants to. Shucks, he can call her Scknnxi Shtoorf if he wants to. But when he sends the book to an agent or an editor, the laughter that will be provoked by either the grossly out-of-fashion name or the silly one will be an impediment to acceptance--the only possible defense (and it may not work) being to launch immediately into some sort of discussion of the name.
I have a bit invested in defending out-of-fashion names, because the name I go by is Byron. It's still in use, but fairly rarely so. And it's very often misinterpreted as some variant of Bryan, which, we all know, comes in the form of Brian, Brien, and even Bryon. When people get my name wrong it can be because they didn't listen closely, don't read by looking at individual letters, suspect I mispronounced it, imagine that I misprinted it, or simply ran into a case where their fingers or their tongue didn't do things in the order they told them to. The fact that Byron is the name of a famous poet could help, but doesn't seem to--possibly because the man in question is a dead white male, hence among the super-sensitive quite out of fashion.
My own investment, however, doesn't interfere with the fact that the name in the story has to fit the situation in the story. Byron might work in a mystery, especially since lots of readers will simply not notice the difference between Byron and Bryon, and can read it either way without hanging up. Mehitabel Arabella, on the other hand, cannot be glossed over, and hence cries out for explanation--and immediate explanation at that.
If you write, you can find books that tell you how to name your characters. I only have one of these (Writer's Digest's _Character Naming Sourcebook_, by Sherrilyn Kenyon, who has a first name that is at least irregular, and might need explanation in a mystery.) Despite some inadequacies, it has helped me a time or two. When I needed a Magyar surname, for example, I found enough of a hint to come up with one that probably works. So far the things I've used it in are all unaccepted, but the name is not likely to be the problem. If you write science fiction the problem is easy to solve: make sure you use r's, k's and th's and consonant clusters of various sorts that suggest the unpronounceable. But we're mainly talking mystery and detection here, and you have to avoid distractions of that sort.
However, what if you don't write mysteries-just read 'em? Well, if you--like me--were raised on phonics, you will be able to go from what you see on the page to some reasonable pronunciation. It may even be what the writer intended. But if it's too out-of-line, you're going to find it distracting. If you grew up with "look-and-say," you read a lot faster than I do, and you won't be vocalizing as you go (I don't mean I actually move my lips, but I do hear the sounds). But you're still going to be thrown by Mehitabel, or Arabella or Aloysius or Henrietta. Maybe even by Byron.
Try not to laugh.
Tolerance is the order of the day: go on until you find
out whether you like the plot, the situation, the characterization, or
whichever of the plethora of preferences you read mysteries for. Laughing
too early can spoil the effect.