Always apply 'terms and conditions' (including rights and disclaimers where required) included within the actual order form the customer signs, as well as having them on your invoices.

Where possible use the same printer for both contact / preview sheets, and the final prints (insuring as much continuity as possible on your part). And where you are using a third party for printing; if there is a time lapse between preview and final prints / reprints, ensure that the printing company maintain records of printing profiles (insuring as much continuity as possible on their part).

If customers are ordering by viewing online, they will need to be made aware that there is a difference between back lit displays and printed formats.

Only to add, as you mention most businesses rely and grow on word of mouth, so always strive to ensure that the customer is happy to recommend you to others. I hope you find a route to resolve the situation to benefit you both.