中文摘要
企业通常既销售基础商品，也销售附属商品。对套牢的担忧促成了针对附属商品的监管，例如价格透明度要求和价格上限。然而，套牢叙事与许多零售情境中附属商品定价低于成本的证据相悖（例如免费配送，或在取消“禁止收取附加费的规则”的国家，银行卡支付附加费的收取仍然有限）。我们认为，统一这些相互冲突的叙事的关键在于，卖方可能会部分或全部吸收附属商品的成本，以免错失基础商品的销售。随后，在附属商品市场拥有市场势力的供应商便会利用这种成本吸收，抬高其批发价格。只有当消费者最初对滴漏价格（drip price）不知情或存在天真认知，且购物成本较高时，才会发生套牢。此时，基础商品的价格会成为滴漏价格的信号，因为基础商品的高加价使企业更加担心错失销售。无论消费者是知情的、不知情但理性的，还是认知天真的，强制要求价格透明并禁止附属商品亏本销售，都会带来（i）附属商品的有效率消费，以及（ii）其批发价格的下降，从而产生严格为正的福利增益。
Abstract
Firms often sell a basic good as well as ancillary ones. Hold-up concerns have led to ancillary good regulations, such as transparency and price caps. The hold-up narrative, however, runs counter to evidence in many retail settings where ancillary good prices are set below cost (e.g., free shipping or limited card surcharging in countries where the “no-surcharge rule” was lifted). We argue that the key to unifying these conflicting narratives is that the seller may absorb partly or fully the ancillary good’s cost so as not to miss sales on the basic good. A supplier with market power on the ancillary good market then takes advantage of cost absorption and jacks up its wholesale price. Hold-ups occur only when consumers are initially uninformed or naive about the drip price and shopping costs are high. The price of the basic good then acts as a signal of the drip price, since a high markup on the basic good makes the firm more wary of missed sales. Regardless of whether consumers are informed, uninformed but rational, or naive, mandating price transparency and banning loss-making on the ancillary good leads to (i) an efficient consumption of the ancillary good, and (ii) a reduction of its wholesale price, generating strict welfare gains.