I am 100% against buying these complex electronics USED.
My reasoning is that I have a 100% failure rate when buying refurbished Denon receivers and pre-pros, even ones that cost > $3,000 refurbished.
I've lost count of the numbers of bad refurbished receivers I've gotten, but it's probably around 4 - 5 units.
So I would buy from a dealer brand new or one of the demo/display models and get full warranty.
This is just my experience.
I have learned my lesson the hard way, but I have learned my lesson to never buy refurbished receivers or pre-pros again.