Dear _____ (name):

In the past I have valued your patronage. But despite the fact that we have
always enjoyed a mutually pleasant and profitable relationship, you have not
placed an order with me in recent (time period). Am I responsible for something
said or done that offended or displeased you?

Please let me know if anything is troubling you that I can rectify. Just call on the
phone so we can talk. I definitely respect your insight and good will.

Cordially yours,