My truck has been in two accidents, neither was my fault. I was rear-ended, and the damage consisted of a dented bumper and screwed up bumper mounts. The repair for this was replacing the parts, cost $1200. The second was a little more involved, as she struck me on the rear pass. wheel. Shifted the rear axle, and dented the box side. Damage was $3800. My point is, it doesn't take much to cause a lot of damage. Both of these accidents were low speed, around 20kph. I wouldn't worry about the collision on the Land Rover. Probably a low-speed accident, and some body panels were replaced. You should be good to go on purchase, and enjoy it for years to come.
As suggested though, I would try to use the collision as leverage to get a better price though. Maybe knock a grand off the price or so.