Looking for genuine offiical tour guide in Beijing

Nee, the safest way is to find a guide through a travel agency. A genuine tour guide has a tour guide certificate issued by tourism bureau. Every year, the certificate is verified by local tourism bureau. In some places, they got new stamps on their certificate. In some other places,they got another IC card except the certificate. The IC card is swiped every year for verification purpose too.

You may require the guide to show you his/her certificate. However, there are some guys who hold expired or fake certificates. It's difficult for you to check it out.