I have set up a guest account on my FTP server, which allows users to upload files to the 'incoming' directory. They are able to do so with no problem, but nothing in that directory is visible to the guest account - not even the files that they just uploaded!
This is the normal behaviour for an anonymous FTP account and it is recommended that you dont change it. At least if your server is connected to the internet.
If you want to change it anyway, take a look at the configuration file of your ftp daemon, there must be some settings for the anonymous accounts.