When selecting an app development agency in Sydney, it's important to consider their expertise in both app design and development. A reliable app development agency in Sydney should have a proven track record with successful app launches and a deep understanding of the latest technologies. Make sure they specialize in the platform you're targeting, whether iOS, Android, or cross-platform. Customer reviews and portfolios can also help you gauge their experience and quality of work. Additionally, consider the agency's communication style and their ability to collaborate with your team for efficient project management. Always check if they offer ongoing support and maintenance post-launch, as this is crucial for the app’s success.