An offer can only be the basis of a binding contract if it contains the key terms of the contract. For example, as a minimum requirement for sale of goods contracts, a valid offer must include at least the following 4 terms: Delivery date, price, terms of payment that includes the date of payment and detail description of the item on offer including a fair description of the condition or type of service. Unless the minimum requirements are met, an offer of sale is not classified by the courts as a legal offer but is instead seen as an advertisement. Under Dutch law an advertisement is in most cases an invitation to make an offer, rather than an offer.