You're making a serious mistake to be specific. One thing you can, and should, do is tie this policy to your ethics policy. In fact, you might want to consider expanding your ethics policy instead of creating a new trap that will certainly catch you by surprise at some point in the future. No one (I hope) plans to do things that are unfair, deceptive, or otherwise injurious to their customers, but as Ken correctly observes, "fairness" is subjective.
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...gone fishing.