If I were in your shoes I would focus on communications to my biggest and best current customers. Let them know you care about them, want to please them and appreciate their business. Next I would hold 3 focus group sessions one with customers, one with non-customers and one with the other credit union members. Ask them what they think, believe about the new credit union. Then I would plan a big public activity for my bank to hit just about the time the new credit union plans to open. DON"T be directing your event to the new credit union, just take a little wind out of their grand opening sail.
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Short cuts to bank revenue growth and higher employee happiness.