People with visual impairments (PVI) must interact with a world they cannot see. Remote sighted assistance (RSA) has emerged as a conversational assistive technology. We interviewed RSA assistants ("agents") who provide assistance to PVI via a conversational prosthetic called Aira (https://aira.io/) to understand their professional practice. We identified four types of support provided: scene description, navigation, task performance, and social engagement. We discovered that RSA provides an opportunity for PVI to appropriate the system as a richer conversational/social support tool. We studied and identified patterns in how agents provide assistance and how they interact with PVI as well as the challenges and strategies associated with each context. We found that conversational interaction is highly context-dependent. We also discuss implications for design.