Ask HN: Ethics of selling domain to prospective client?

I recently petitioned a local business to freelance design/develop a site for them. Ahead of our first meeting, I did some domain searching and found a great domain name (it's a domain hack).

I feel that the domain could be worth something on its own, but I'm not sure that it's ethical at this point to try to sell it to them. Do I give it to them? Give them the option to purchase it (cost?)? Solicit to a larger brand? sit on it? I would've never have found it if they didn't appear interested in having an online presence.