Buyers pursuing unavailable sellers is a common source of inefficiency in matching markets. We report the results of a field experiment in a large online marketplace where sellers could pay to signal higher capacity via a badge that simply said "available now." All sellers could rent this signal but only randomly treated buyers could see it. We find that sellers who rented this signal were positively selected, treated buyers sought them out more, and as a result matching efficiency increased. We discuss why costly signaling is necessary to facilitate this coordination, and show that mere statements about seller capacity had become uninformative in this marketplace. Two years after the experiment, we show that sellers renting this signal continue receiving substantially higher buyer attention. The full version of the paper can be accessed at https://apostolos-filippas.com/papers/costly-capacity-signalling.pdf.

We study the introduction of advertising in an online labor market where applicants could bid to "boost" their applications. Applicants with the highest bids received a prominent position at the top of the employer's application list. The platform randomly varied whether the employer was exposed to boosted applications, and within the exposure group, whether the employer was shown a disclosure that the application was boosted. We find that boosted applications are positively selected, and that boosting an application increases the likelihood of an applicant being hired by about 40%. The experimental design allows us to estimate that about 80% of this increase was due to the ranking effect---boosted applications ranking higher---and 20.2% was due to the signaling effect---the disclosure that the application is boosted. The full version of the paper can be accessed at https://apostolos-filippas.com/papers/boosted.pdf.