Welcome to the MLF!
Zero turns are definitely nice machines and can cut the average mowing time in half vs. a tractor.
I don't personally know much about the particular model, but I did pull some links that you might find of interest. Depending on the year of it, it looks like it's priced competitively from what I pulled up. More specifically, you could see if there are similar ones for sale in your area to narrow it down even more for an even better comparison.
CUB CADET Z-FORCE, Used CUB CADET Z-FORCE, CUB CADET Z-FORCE For Sale At TractorHouse.com - Page 1
I would ask the owner what kind of maintenance that's been done and ask to see any paperwork that goes along with it. I would test drive it, test all the functions and see how it opperates and perfoms. Other things to ask are things like:
1. Has it been stored indoors?
2. Any known issues or problems that it's previously had?
3. Are you the original owner?
Take a good look at the machine and inspect it's overall condition; belts, blades, tires etc. It should give a decent indicaction of how well it's been taken care of. It should look fairly new being that it has low hours.
First take on my Cub Cadet Z-Force 50 - TractorByNet.com
Cub Cadet Z-Force® 48 Zero Turn Rider, ...A very sharp incline mower!!! - Cub Cadet Z-Force 48 Zero Turn Rider - Epinions.com
Cub Cadet Z Force S 48 17AI5BHB information from Consumer Reports
Cub Cadet Recalls Riding Lawn Mowers Due to Fire Hazard
^ It looks like there was a recall, so if you go to look at it, I would ask if it's been done and any paperwork they can provide that documents it.
Keep us updated and hope this helps some.