My SO has that problem, but I never encountered it myself.
It seems that Nook, when someone moves out, will auto fill the spot left with a random villager, and that in usually 2-3 days, sometimes even the day straight after the villager has left.
That makes her mad because she wants to find the perfect villager, but gets stuck with a random villager before she could do a good amount of mystery islands to find it.
So is there a way to tell Nook to not auto sell the spot? (Or is there something that she does that it 'auto sells' the spot or at least looks like that)
Best Answer
Short answer no. Nook will eventually fill empty plots.
One thing doable is to not build all the spots if it's not already done, recruit a wanted villager on an island and only then build the plot.
I couldn't find a source apart from my own experience, feel free to add one.