A Certified EOS Developer is a skilled coder who is experienced in coding in EOS based blockchain platforms and able to launch, test, debug and upgrade such systems. A EOS developer can work with the companies and consult how they can benefit an EOS platform-based solution instead of Ethereum or Bitcoin-based platforms which have reportedly lesser transactions per second as compared to EOS.
EOS developers are quite rare to find giving them a high chance to earn more as compared to other blockchain developers but then again it depends upon which industry/company you are going to. A certified EOS Developer has a good potential in current space as a certification provides better recognition of skills and makes it easy to pick up freelancing projects.