For instance, human eyes can't perceive the difference between a 12MP and a 50MP image printed in a poster format from a typical 1.5-2meters viewing distance and 8MP is usually good enough for most large prints.
So I would advise choosing a second hand model taking shutter count, general state, lenses quality, autofocus speed and image stabilisation efficiency as more prioritary parameters than sensor pixel count.
On one hand, you have to remember that huge MP doesnt do much if the glass can't resolve well enough.
On the flipside, I have to note that switching to high MP full frame makes it a lot easier to do good, clean crops. Sometimes I might care about a small portion of the frame but for composition reasons (e.x. can't get closer for one reason or another) I at least can lean on cropping more.