Offers may either be firm or _______ . A firm offer, also called offer with engagement, is made when a seller promises to sell goods at _________ and within a stated period of time known as _________ . A firm offer holds the seller responsible for the business once it is accepted by the buyer. In a non-firm offer, at times called offer without engagement, it is ____________ by the seller after being accepted by the buyer. When offering, this must be made clear to avoid possible ___________ .