分析下原因,一般情况下我会再写封追踪信给他:

Hope you are fine, my friend.

It is regret that I haven't receive any information from your side. May I have your idea about our offer? We will try to satisfy you upon receipt of your reply. As we don't want to lost a good customer like you!

If there is anything we can do for you, we shall be more than pleased to do so. Hope we can build good cooperation with your.

如果客人还没有回信,一周后再问客人不回信的真实原因.(一般情况,70%的客人会告诉你他的原因)

Glad to contact you again!

Have you kindly check my offer? Hope they are workable for your market! Sorry that we still don't receive any information from you. I would apprreciate for your any comment about our offer, including price, quality, sercive. No matter if it is positive answer, It is great help for us to meet your requirement.

Waiting for your favorable reply soon!

之后的日子里,可以尝试新产品的报价,刺激下客人的神经.

我通常是这样写的：
good day!
my quotation of digital photo frame you might have received and considerated. could you kindly advise your comments at your earlier convenience?
if the products isnot your are   expecting,pls advise me your details requirement, i will re-offer asap.
i am of service at any time!
但是，不同的客人，我会变换着写邮件，让客人知道我们公司，产品的存在．我不会把客人缠得太紧，约十来天给他一封邮件我通常这样回复的：
Dear ***,
Wish you have a nice day!
May I ask whether you have received my quotation?Now I am sending it again,if you have any other ideas.Please feel free to contact me.We will do much better if you can give any advices to us.
I am waiting for your reply ASAP.
Best regards
但是，想成功可不是容易的事情．

dear sir
have you received our quotation of ..., if you have any further question,please don't hesitate to contact us.we are waiting for you comment about our quotation.

we hope that we can establish a good business relationship with you in the nearest future.

your prompt reply will be appreciate.

回复A：直接去函敦促 Dear Hugo Chu, Wish everything well with you and your esteemed company ! We are in receipt of your letter dated Aug 10 , and as requested was expressed you 3 catalogues for our refrigeration goods . We hope they will reach you in due course and will help you in making your selection . Wish we will promote business as well as friendship! Best wishes ! 

回复B： 先写邮件问清情况。本人觉得先写邮件问清情况，简单的询问，如HAVE YOU RECEIVED MY P/I, IS THERE ANY QUESTION OR PROBLEM WITH YOU? 再问何时开L/C 或汇订金过来.....如客户没回复，那你应该(很有必要)打个电话过去问清情况。是价格问题还是临时发生改变? 客户是中间商，还在等最终客户的确认？还是其它问题？然后根据情况做一些措施看能否挽回这一张订单。 Dear Sir, Good morning! Hope you have got a wonderful weekend! For several days no news from you, my friend. Now I am writing for reminding you about our offer for item of **** dated ** ** ** according to your relative inquiry. Have you got (or checked) the prices or not? ( You can add some words to introduce your advantage of your product or something else to attract the customer). Any comments by return will be much appreciated. It will be our big pleasure if we have opportunities to be on severice of you in near future. Looking forward to your prompt response, Thanks and best regards, Yours Faithfully

回复C：如果仍然没有回音的话，可以在一、两个月后再写一封信。 Dear Sir, Now I am writing for keeping in touch with you for further business. If any new inquiry, welcome here and I will try my best to satisfy you well with comptetitive prices as per your request. By the way, how about your order (or business) with item ***? If still pending I would like to offer our latest prices to promote an opportunity to cooperate with each other. Thanks and best regards