They shoot, well, about the same as any other good quality double. Expect short chambers, and tight chokes. No issues on correcting either, but, do have a good gunsmith do the work, as opposed to a local 870 mechanic. If it breaks, you are SOL, and will have to, again, pay a good gunsmith for his skill in reverse engineering a replacement part. The very good news is the only thing I have ever seen break in a Charlin (I've handled a lifetime supply of them) is a little flat spring that keeps upward pressure on the toggle when the gun is cocked-if the gun goes "clunk, clunk" when you cycle the action, this is the problem. Doesn't sound like an issue, in this case.
Dating a Charlin, isn't possible. There, I've said it. The company was owned by several owners, and serial numbers, and sequence didn't mean a lot to any of them, from what I've seen.
A Charlin, like a Darne, can be left with the action slightly open, which, will function just like the safety everyone complains about-the gun can't fire. Where a Charlin differs from a Darne is that the breech is not locked to the barrels-the action is an over-the-center device, and pressure on the breech face tends to hold the action more tightly closed. It is a clever arrangement, but, more then one bloke has stuffed standard, American, high pressure ammunition into a short chambered 5 1/2 lb Charlin, and peed his pants after the shot, when he saw the opening lever slightly lifted. But, nothing is wrong, the action is just protesting the abuse. The gun can't open. That same reason is why I prefer a Darne for my slidey breech guns, but, that is just me. A Darne, is one bolted shut tight mother when the key is closed. I like it that way.
Price pretty much comes down to how much you want it. None of your friends will have one, so they won't have gotten a better deal then you, which, might cause undue embarrassment, if that 'sort of thing bothers you. I always liked the sling swivels that all of them seem to have, but, you could and should use that as a ploy to get the price down-I have. If the price is too high, wait a month, and then start waving cash at the owner-the gun will still be there. Probably still be there in a year, in all honesty.
Good luck, and let us know what happens. If repairs or an inspection are needed, Kirk Merrington is your man.
Best,
Ted