Trust is essential for beginning and maintaining relationships online where assessing uncertainties and risks is difficult. While product delays have been shown to reduce trust in e-commerce settings, we understand little about the effect of delays on trust in the increasingly popular context of crowdfunding. In a mixed method study, we examine what factors influence backers' trust in crowdfunding when rewards are delayed. Based on in-depth interviews with crowdfunding participants, we found that a rich set of factors influenced backers' trust including backers' role identity and domain knowledge, backer's research on a creator's background, creators' communication during delays, and duration of delays. To better understand the factors affecting delays, we conducted a regression analysis with 4,089 delayed projects and found that the funding goal, number of backers, percent raised, number of reward levels, and creator's previous crowdfunding experience are associated with the duration of delay. We discuss design implications for managing delays and maintaining trust in crowdfunding.