Dear John - your prompt contact is appreciated.
I ask a favor from you- if you receive another offer for the domain name, please let me know so that my client is presented the chance of considering matching or doing better than that offer. I cannot guarantee that would happen, but they would like the chance to bid.
请不要用翻译软件简单的翻译,我已经这样做了,因为意思不通顺,所以才请大家帮忙