From Seth's Blog:
It's okay to treat some customers differently, but first it pays to figure out who you're dealing with and why you want to re-allocate your resources.
I'd go as far to say it's impossible to treat all customers the same even if you wanted to. Customers who contact your customer service are getting 1-on-1 service that the others aren't.
Just be honest why you're treating customers differently. Because they had a problem, because they paid us the most, or because they are the loudest are all valid responses.
Eric Davis
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