[edited by: Webwork at 6:52 am (utc) on Dec. 5, 2007]
[edit reason] Per Charter please avoid specifics of your domain names [/edit]
Make sure your agreement indemnifies you against any legal liability.
Make sure the buyer has the financial capability to indemnify you. And make sure you know who your "buyer" really is. Are you sure it isn't the celebrity, or their attorney?
Lock the money away, and don't spend it - just in case. Hope for the best, but expect the worst. Consider the possibility that the deal may wind-up *costing* you money.
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Or....
Take a deep breath. Talk to a lawyer. Ask yourself if it is fair, reasonable, and legal for you to trade on the name of a famous celebrity, and make sure you understand the intellectual property laws of your country.
Then consider the publicity value of simply handing the domains over to them at no cost.
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Whoops, I didn't answer your question.
They're worth what the buyer is willing to pay. If they're really a buyer.