To evaluate the portfolio of a mobile app development company, I suggest assessing the diversity and quality of the developed apps by the mobile app development company. Check for innovative mobile apps with excellent user interfaces and smooth performance. Look for mobile apps focused on various industries and sectors, which can indicate versatility and adaptability in their mobile app development services or website development. Also, keep an eye on mobile app ratings, reviews, and download numbers on the App Store for iOS mobile app and Google Play Store. The company's success in launching high-quality mobile apps is a crucial parameter for evaluation in the mobile app development services industry.