Independent review communities are the best way to cross-check a provider or venue before spending money on it. The forums below have been around for many years. Note that most of them are blocked within mainland China — see our internet access guide for how to reach them from inside the country.
theeroticreview.com is a huge database of escort reviews from all over the world. Registering and reading reviews is free; the more interesting content is reserved for VIP members, a status you can reach either by paying or by contributing reviews yourself.
The International Sex Guide — nowadays at internationalsexguide.nl — is a popular forum where members post field reports from all over the world, with active China sections. Posting reports and comments is free, though everything passes through moderation, and some features such as private messaging require a small paid membership.
The English-language Sex141 forum — formerly at forum.sex141.com, nowadays at forum.141-161.com — is another solid place to find reviews. Its main audience is Hong Kong, but there are subforums covering mainland China. It uses a level system: certain content only unlocks once you have contributed enough posts and reviews of your own.