Pickup & Ohms
 

I saw a used pickup with 8.5 kOhm and another pickup with 16.5 kOhm. I know that this is resistance but ... these numbers dont say anything to me. What does this mean? Is that good, bad? how do they sound...? Whats important to know when buying pickups'

On their own, those numbers mean shit.

Assuming identical design and specifications on both these pickups, on a superficial level, the one rated 16.5k will sound louder and darker than the one rated 8.5k.

However how it'd'll sound will be affected by things like the magnet used, the wired and gauge, the bobbins, the winding etc. many many other factors will affect how a pickup will end up sounding, the resistance ratings mean very little on their own, other than telling you the output level, but even that is not always accurate.