Digital Proofing--Proof Positive
Ask your vendor to help you arrange seminars or demonstrations for your customers where this type of information can be illustrated in detail. Show and tell is perhaps the best way to demonstrate the accuracy of the digital proof. It may take a little time and investment on your part because you will have to run a press proof, an analog proof and a digital proof of the same images or pages. But having samples for comparison will be well worth the effort.
A final thought: With the technology that is available today, showing the accuracy of the digital proof should not be difficult. If, however, you are using an older technology that does not generate a totally accurate match, consider this. What really makes a proof work depends to a large degree on the relationship and flow of communication you have with your customer. Did you rely on the analog proof because it was so accurate or because you taught your customer how to read it—that the reds would be a little less brilliant or blues not quite as royal?
It's up to you to teach customers how to read a proof. In the end, the real contract is the trust between the buyer and printer, and not about ink on paper.