It's missing the rear sight, and rust on the lock might mean rust in the barrel, or worse, fouling and pitting that's been busy in there for goodness knows how long. If he were able to show clear bright photos of inside the lock and inside the barrel a better assessment could be made - without knowing the bore it would be in the $100-$200 range, if it's nice and
clean inside but just externally a bit poor, $200? Maybe $300 if internally pristine with bright shiny bore, but that's the top end. If that's just old dirt and dust on the action then a good cleaning will increase value. Also looks like the front sight is a bit odd and there's some bluing wear or something - that would need a clearer picture to get a better idea.