It really comes down to what you are looking to do with it. If you like the Chargers and want to build it for yourself, that's one thing, but you are going to put a LOT of money into it if you are looking to rebuild/restore it (as you probably know).
Me personally,.... I'd be a little leery of a guy who puts one picture in the ad, no description of condition, and throws a price of "$18K Firm" on it. If it is close enough to you to go look at it, it never hurts to go look. If it is a standard Charger with no special options and not numbers matching, you will likely put more into it than it will be worth, though the '68-'70 Chargers are incredibly popular and pulling good prices, even for non matching standard cars. Big block helps, even if it's a 383 2bbl. Not much to look at, in regards to the number of pictures, but the hanging rocker trim signifies it could be an S/E car. That helps as they really didn't make as many S/E's as they did standard Chargers or R/T's. I believe the rocker trim was one of the distinguishing features of the S/E. That and leather inserts on the seats, stainless trim on the pedals, and woodgrain dash bezel. (My Charger I am getting rebuilt is a 69 S/E that was originally a 383 2bbl).
In regards to your questions:
1) Yes,... you want it to be complete as possible, though you will like be replacing a lot of components anyway, or at least having them redone. Having all the trim would be nice, but that depends on condition. If it's there, but all dented up, you will spend a bunch to have it straightened and polished, or end up replacing it. Fortunately pretty much all of it is available. Interior is somewhat important, especially the dash components as I haven't been able to find some things like the center A/C vents.
2) Running and driving always helps. That allows you to work on the mechanicals first to get it reliable enough to get it out on the road and have fun with it while you are fixing things here and there. If you are planning to rebuild the whole car though, you'll likely rebuild it all anyway, but at least if it runs and drives, you'll know you aren't missing a bunch of parts.
3) Check the frame rails closely. Rotted floor pans and trunk can signal rust issues in the frame rails, but not necessarily. My trunk and floor pans were shot, but mine was an undercoat car and the frame rails turned out to be solid and relatively clean. The shop working on mine had to replace some of the floor supports, but the rails themselves were good.
4) A good interior that can be cleaned up is worth a lot. Pricing on my full interior soft goods (Just the seats, door panels, upper door pads, carpet, and headliner) is adding up to about $5-$6K (List price anyway,... Hoping to get a good discount from a show or something).
In my opinion,... After seeing what these are going for.... If the car runs and drives, the interior is nice enough to be cleaned up and useable, at least for now, and there are no major rust issues, I would say the car is worth what he is asking. I've learned that metal work is key. That is BY FAR the most costly part of the rebuild, especially if you will be having someone else do it!!
