Honesty is the best policy in life and same for business. I don't see it ending well at all if you have said you'll broker it for them, all is not lost though be upfront about it and tell them you own the name and see how it goes from here, as far as price is concerned it is your domain (which we don't know), they have cctld which means they'd be leaking traffic and emails as well plus as you say they're wealthy so there's certain need for them to acquire it. Consider all these factors along with how much you want for the name, best of luck for the deal but once again if not today later on you always regret lies.