IF you do not know the person and they are not friends or family I personally don't see how this is a moral dilemma for a domain trader.
You don't reg it because you are being an arsehole you reg and profit from it because that is your business.
You snooze, you lose.
I don't think you should put a higher than realistic sale price on it but I see no moral dilemma in trying to sell it to him or using it for the traffic if he does not want it.
This is all assuming, of course, that TM is not an issue.
I'm actually baffled to hear that some of you see a moral dilemma here. I just don't see it.
However, I do think that it would be a moral dilemma (for me) if you do not offer to sell it to the hyphenated owner at all because you want the PPC money (if it's significant). I think he should at least be given the chance to buy it from you if he sees the value in it. If he refuses becaue he thinks it is an unethical move on your part, he misses out and you profit from the traffic that forgets his hyphen.
It's all business and should not be taken personally. Domain tradering is legit and you gota put food on the table.
It's like buying the .COM of a person who owns another extension of that domain. There is no moral dilemma there for most of us, I think, and therefore there should not be one in this case.
If it is a friend or a family memeber, then you should reg it and give it to them as a holiday or birthday gift. I think that would be a great gift to a website owner. reg it for a few years instead of just one.