Where to find good PCB partner

We are a professional PCB manufacturer in China, all of our boards are exported all of world.Now, during our more than 10 years development, we find that although we have many customer from oversea, there is only 10% customer is partner, others are not, from our record, we found 80% customer is unstable, theirs order quantity is also not very large, what's reason for this? And how we can keep more customer as long term partner? Can any one give some suggestion? Thank you.

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Shenzhen Kinji Electronics Co.,Ltd
Tel：86-755-83585818 Ext:227
Fax: 86-755-83585267
E-mail:lindy@kinji.cn
Webpage: www.qjpcb.com
MSN: lindy101555@hotmail.com
SKYPE:lindyzhoupcb
Mobile:86-13682606904