Hi Kevin,
I suggest to:
1. Get the VIN and use Carfax or a similar service to see where this car had been and what it's done. Hopefully it's possible to do that for cars outside the US as well?
2. Check whether it's full charge or 80%, if the owner knows anything about the car they should be able to tell you.
3. After you ascertain it's 100%, look at how many white bars light up in the graphic to the right of the range number. That's the quickest indicator of battery degradation, and it's more meaningful than the number of km showing as "range" (we call that number the "Guess-O-Meter", because it's just an estimate based on the last few minutes of driving). I'm talking about the wide white bars in this image:
A brand-new battery has all 12 bars, and the decrease is roughly proportional, but discrete (i.e. one bar each time you hit a threshold). So if, say, there are only 11 bars at 100% charging, it means the battery only has roughly 92% +/- a few percent capacity remaining. If there are only 9 bars, then the battery is about one-quarter degraded. The picture above has 10 bars, which might mean either that it's not fully charged, or that it's lost capacity. Maybe I'm wrong on the exact figures, but you get the idea.
Leaf batteries do poorly in very hot regions (>40C on a regular basis in summer), where some lost nearly half the capacity over a few months; there was a lawsuit and Nissan replaced batteries or compensated, so you shouldn't get this kind of Leaf there. Elsewhere, you shouldn't expect to lose more than one bar per 15k miles, or even more slowly than that.
4. I think if you have 11 bars or more, your daily trip is very doable, although you'd probably want to tone it down a bit to 50-55 MPH rather than 55-60. The Leaf loses range very drastically at higher speeds, see a chart here: http://www.mynissanleaf.com/viewtopic.php?p=101293" onclick="window.open(this.href);return false;
5. Last but not least, if you mostly charge at home at night you'll need to install a dedicated Level 2 charger. The "trickle" cable that comes with the car and connects to regular household outlets, can only replenish some 60%-70% capacity over 12 hours, so you'll always be on the cusp or worse.
Last but not least, feel free to bargain hard, esp. if they don't provide much information! I wonder how much they are asking for?