Rebecca,

Countywide Abstract, Inc., went through this very thing beginning in May, 2004.  One of their very large clients ran into some difficult times.  After a few months of continued orders with no pay, CWA's President, Francine Miller decided enough was enough (it is important to understand, however, the level of communication in this scenario was almost nothing.  Orders came, but no returned phone calls or responses to emails, etc.), she allowed her staff to process two large commercial searches and held them.  After NOT meeting our standard turn-around-time of three days, sure enough, they called.  Francine simply stated that she was going to hold these searches until full payment was received.  It was a huge gamble.  It could very well have ended the relationship entirely, thus sticking the company with a HUGE outstanding invoice, not too mention current invoices.  HOWEVER, when do you pull the plug rather than continuing to allow a client to get farther and farther in debt to you? 

Re-examine the relationship you have had.  Be certain is has nothing to do with you and/or your service.  Once done, try to remember that orders are great and we all want a lot of them, however, all orders do, until payment is received, is put YOU deeper and deeper in debt.  Best of luck.....JT