What is the most popular local forum in Shenzhen?

There is a forum on the Shenzhen Real Estate Information Network, but there are also many intermediaries and there is a commission-free section, which is worth trying.

From personal experience, it is best to go directly to the community of your choice to find a notice or to consult with security guards (including shop owners in the community). As long as you have a house, the chance of success is quite high. Under normal circumstances, it is enough to give the security guard some favor money, and the amount can be discussed. If you are really unfamiliar or have no experience in interacting with people, you can find someone to go with you. This will take time and is more laborious, but I think it's worth it. I've saved a lot of agency fees, and more importantly, I'm quite satisfied with the house.