Do I have to find an agent to rent a house in Guangzhou?

If you can find the owner directly, of course, you don't need an intermediary.

Or pay attention to whether there is any relevant rental information on Guangzhou real estate online.

It's your first time in Guangzhou. I suggest you go to an intermediary for consultation.

There are many intermediary houses. You can make a comparison. But the only bad thing is to charge an agency fee.