Crowd accessibility services for people with disabilities, driven by crowd-sourcing methods, are gaining traction as a viable means of realizing innovative services by leveraging both human and machine intelligence. As the approach matures, researchers and practitioners are seeking to build various types of services. However, many of them encounter similar challenges, such as variations in quality and sustaining contributor participation for durable services. There are growing needs to share tangible knowledge about the best practices to help build and maintain successful services. Towards this end, we are sharing our experiences with crowd accessibility services that we have deployed and studied. Initially, we developed a method to analyze the dynamics of contributor participation. We then analyzed the actual data from three service deployments spanning several years. The service types included Web accessibility improvement, text digitization, and video captioning. We then summarize the lessons learned and future research directions for sustainable services.