We get written permission. This came in handy once, when we were called by someone asking for the customer's info and we said we had to get permission first. When we called the customer, he had no idea where this call was coming from, and I feel we prevented a possible identity theft.
Our customers also like the fact that we are showing the effort to keep their private info private.
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Member of the National Sarcasm Society - like we need your support!