Final answer:
In trade-in advertising, the word "guaranteed" should not be used, as it implies a promise of a certain trade-in value for all customers, which is misleading.
Step-by-step explanation:
When advertising an allowance for a trade-in, certain words are regulated due to the potentially misleading promise they imply. Specifically, the word you cannot use is "guaranteed". This is because a guarantee suggests a promise that every customer will receive a specific value for their trade-in, which is often not the case since trade-in values can vary significantly based on the condition, age, and market demand for the used vehicle. Words like "unlimited," "free," and "exclusive" may also have restrictions depending on the context, but "guaranteed" is most commonly prohibited in this scenario.