Private guide in Athens

There are a number of both private and small group tours on TripAdvisor - you might start your search there. We've usually found their reviews to be pretty accurate.

You will find a list of official licensed guides here

https://www.tourist-guides.gr/

Only these licensed guides are authorized to come with you to the sites and museums.

Local companies offer private or group guided tours:

https://www.alternativeathens.com/

https://www.athenswalkingtours.gr/

There is no point in booking on sites like Get Your Guide, Trip Advisor, Viator, etc. since these websites are just middlemen who will charge you extra.