Strata Schemes Management Act 2015 says that the appointed strata manager “must hold a strata management licence issued under the Property and Stock Agents Act 2002”. You can google “NSW strata management licence” and see if the agent you are interested in holds a strata management licence.
Perhaps ask your friends and colleagues about their own strata manager? I recently went through the process of getting quotes from strata managers. I made up a spreadsheet to compare costs.