With respect to what you should do:
I would send him or her an e-mail as soon as you decide on your price, and tell him or her that the offer will be good for a certain time period.
You also want to decide if you want to use Escrow.com to handle the
transaction. If so, include that information and the price with a link to Escrow.com. You will need to decide if you, the client, or both of you will pay the escrow fee.
For example you can say something like this:
(e-mail content within dotted lines)
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Thank you for your inquiry about the domain name ChristianCenters.com.
The price of the domain is $295.
Escrow.com will handle the transaction, and the escrow fee will
be split 50/50 between the buyer and seller. The overall escrow fee
will be about $25, so the split will be about $12.50 buyer/ $12.50 seller.
For additional information about Escrow.com, please visit their website.
(Add link here)
This offer is good until 10 pm EST on June 5, 2004.
If you have any questions, feel free to e-mail me.
Thank you.
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The client may then respond with a counter offer, and you can decide
whether you want to accept it or send him or her a counter offer.
Good luck.
Take care,
Kevin