Hi Karim - totally agree with you that domain investors and resellers are a thing, and if done right (in volume or with very highly sought-after keywords), can be a very profitable business - it's just not a business I'm in. And I also agree that he didn't do anything wrong, but if I were less savvy about SEO and how the traffic we brought to the site increased the value of the non-hyphenated version, I could have paid for something that only held value thanks to other work I had already paid for. I also do see the value in owning multiple domains (if done right, this can help a company own an entire space online and/or up their SEO rank - but it's not so simple as purchasing a bunch of names, flooding them with keywords, and slapping on a redirect).
Not 100% sure if being a woman helped or hurt me in this negotiation - but I think it was an advantage, mostly because I think he thought my guard was down and my knowledge was a bit lacking. And that I was gullible and not-so-tech-savvy. And I was fine to let him think that, initially. :) Just my preferred method of negotiation, but of course it isn't for everyone.