Absolutely - you need to take a stand with your client.  This wishy-washy well they might not send me another order if I do is ridiculous.  Just be short and sweet - you ordered it, I ordered it, it was done before you cancelled.  Maybe the next time they will wait to order it from you until they know the order is a good order.  They need to suffer their own losses - its part of being responsible for yourself.  Do you always take on the responsibility of another person or entity?  That is not a healthy personality trait.