As Stick said, what make/model and what price are you looking at. It may be 'slightly' used but an older model which may be hard to find accessories and part for.
I presume it is a plunge router.
Turn it on for a few seconds to make sure there is no bearing whine.
Plunge and release a couple of times to make sure the plunge is free and positive.
Move the speed control back and forward to listen for speed changes.
Make sure the collet is working and you have the correct spanners.
When I bought my second hand 3600BR , it broke all those rules but I was able to resurrect it from the scrap heap... [ I only bought it for parts, but now it is an important tool in my arsenal ]
I don't mind if other members disagree with my comments.
I don't profess to know everything, and I may learn something new.
"Never attribute to malice that which is adequately explained by stupidity."