If you're not sure if a file is fake or not, it helps to browse and whois the users in the group. Check if they are sharing the same files, and if they all have 3000 files (not all flooders have 3000 files, but most do)
The flooders also make stupid names on the movies, such as:
some+movie+name
some movie name (2) (4)
some-movie-name
If a user is sharing a lot of these, then this is more than likely a fake file server.
The recording companies have also started with other dirty tricks - share fakes along with the real files, so you may get a group with a bit of both..