IDEA: Tell key customers how to contact you after-hours. Handout telephone numbers to use 24/7, specifically just for them.

Your customers will normally not call you but hand them cards with telephone numbers to call after your closing hours.  You are committed to their satisfaction and will try to help them after hours or weekends if at possible.  Chances are they will not call you but their buyer will feel better knowing he can contact you directly and get an answer.   Train your staff in the case the customer does call in the evening or over the weekend, to take the call, be pleasant and helpful, take their number and then call for directions from supervision before sending hourly employees to assist.  Allow management decide how important the customer is and what can be done to make him satisfied after responding afterhours.