Which of the following is not considered an unlawful practice for a seller?

The correct answer is that failing to call or email the buyer with a promotion is not considered an unlawful practice for a seller. This is primarily because promotional communications are generally at the discretion of the seller. There are no legal obligations requiring a seller to reach out to customers with promotional offers. Promotional activities can enhance customer relations and potentially boost sales, but they are not mandated by law.

In contrast, the other options represent more serious obligations that sellers have towards their customers. For instance, not providing a completed receipt or contract copy can lead to major issues regarding transparency and consumer rights. Similarly, failing to inform the buyer of their right to cancel is a violation of consumer protection laws designed to ensure buyers understand their rights in a transaction. Lastly, refusing to honor a valid notice of cancellation breaches established agreements and consumer rights. Thus, these practices are indeed considered unlawful.