In my county in Texas, no one actually enforces this. I called the enforcement folks one time, but they could not answer my question. I have never heard of anyone getting in trouble. I agree with Andy--you should check your state laws, but probably you do not have to make it as easy as it is for customers. Having them write for an entry form and include a SASE is one way to allow them to play, but not make it so easy. I'd probably recommend something on the website that gives them the address where they can write to request an entry form. However, if you do, you may want to limit it to adult residents of your service area if you can. No use giving something away to someone with a computer in Taiwan.
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Better a patient man than a warrior, a man who controls his temper than one who takes a city