I had watched Craigslist and other local sellers for about a year, trying to find an F12 in good original / used condition, while doing my research on new stoves. My preference was to find a new stove as nice as the F12 (in my opinion, of course), a catalytic stove with pretty iron outsides. Blaze King had been teasing the Ashford for more than a year, forever shifting their release date, and I got sick of waiting for them. I could not find another cosmetically acceptable catalytic stove of similar size with a top flue.
So, I just bit the bullet and plopped down $1500 for a "rebuilt" F12, from a guy who sounds a LOT like your seller. This guy had a seasonal job, and spent his off season rebuilding and reselling old wood stoves. Since there's not much $/hr in a business like that, he did the minimal amount of work on every stove, to make it pretty and get it out the door. Within weeks of bringing it home, most of the gaskets fell off, because he used clear cement on grapho glass gaskets. I pulled the front door and top load gaskets, and replaced with proper braided fiberglass and black silica gasket cement, and haven't had a problem since. The damper was out of adjustment, but easily fixed. The only thing I found that really bothers me is a crack in the iron top, under the top load door. It hasn't been a problem yet, but I'm on the lookout for a new top, as Jotul no longer sells that casting.
The Firelight 12 is a fantastic stove, but being older, a risky proposition for a first-time burner. We answer hundreds (thousands?) of posts here every year, from new burners having trouble with their stoves. Until recently, some of those trouble posts were my own. One problem with a newbie shopping used stoves is that you may miss critical details when inspecting a stove to buy, but the other problem is that there will be many questions about wood vs. technique vs. installation vs. a malfunctioning stove, when you have the inevitable beginner's troubles.
One thing you'll learn around here is a lot of folks swap their stoves out pretty frequently. Once you have the chimney installed, and catch the hang of this, you'll see it's not nearly as big a deal as the initial installation. Set up your hearth so that you're exceeding minimum hearth pad size, etc., and you'll have the flexibility to install any stove on there, down the road. Then get yourself a stove that's going to perform right out of the box, even if you think you'll be lusting for that Firelight 12 down the road. Get over the hump of the first two years, and you'll be in a good position to hunt down a better used stove.
BTW... I'm not sure I'd have bought the Firelight 12, if I didn't already have one at the other end of the house. A big part of my decision to go this way was interchangeability of parts. If one stove breaks, I can steal parts from the other to get it back up and running. One of my stoves is in the 4-story end of the house, the other stove is in a 1-story part of the house... guess which one I want to keep running? In any case, some parts for these older stoves are only stocked at Jotul headquarters (Norway), so it can take a few weeks to get things if something breaks mid-season. Having two of the same stove eliminates that issue.
... and before you ask, "what could break," search out my old post on a squirrel getting into my first F12. It destroyed my internal refractory, and shut me down for 6 weeks right in Jan/Feb of 2012.