購物網站低標價格，於消費者下單後拒不出貨，曾引起軒然大波。法院對於購物網站之下單機制構成要約還是要約之引誘，未有定見；對契約若成立能否撤銷，沒有詳盡說理。援用經濟分析理論，本文主張若購物網站之使用條款已經將其下單機制界定為要約之引誘，則應作此認定。縱使認為契約成立，是否容許購物網站撤銷意思表示，應個案考量表意人與相對人之過失程度；而此過失之認定，不應援引抽象或具體輕過失之概念。主管機關經濟部在標錯價事件後公布之「應記載事項」，昧於市場交易之現實，過度偏頗特定類型消費者，無怪乎主要購物網站明白不採其規定。但若主管機關堅持貫徹其規定，消費者之整體福祉不增反減。 There have been several disputes regarding the on-line retailers who quoted a below-market-value price but refused to honor the ＂offers＂ by consumers. Taiwanese courts do not have consensus on whether the purchasing mechanism in the on-line retailing website counts as an offer or an invitation to make offers, If the said mechanism is regarded as an offer, the courts are unable to decide whether, the retailers may revoke the contract. Using economic analysis, this article argues that if consumers consent to the end user agreement that stipulates that the purchasing mechanism is only an invitation to make offers before making the purchase, then courts should generally honor the agreement. If, for whatever reasons, the purchase contract is considered valid, whether or not the retailers may revoke the contract should depend on the mutual mistakes by both sides, rather than on the unilateral no-fault condition on the retailer’s side. The Ministry of Economics has intervened in the consumer retail market by stipulating model contracts that all on-line retailers have to obey, and yet a few stipulations have gone too far and hurt all consumers in general, causing major on-line retailers to ignore such mandatory stipulations.