Final answer:
Mavis's posting of her motorcycle for sale on an online auction site is considered as an invitation to negotiate rather than a legally binding offer.
Step-by-step explanation:
When Mavis posts her motorcycle for sale on an online auction site, this action is considered d) an invitation to negotiate, not an offer. An invitation to negotiate is a preliminary communication indicating a willingness to discuss the terms of the sale, but it does not constitute a binding offer that can be accepted to form a contract. Instead, it invites potential buyers to make offers, which the seller can then accept or reject. In contrast, an offer is a clear and definite proposal made with the intention that it becomes binding upon acceptance by the person to whom it is addressed.