Well, yeah... This is just an opinion from a random newb. So, you can ignore it if you want.
The tryout system, although can prove to be successful, also has its downsides like what did Timbjerr and Yuoaman said. However, this loophole can be avoided with constant watching from the upper sides and normal members.
Sometimes I wonder: "How hard it is to pick a Moderator on a Pokemon Forum? Modding Forum can do them in no time". Now all seemed more clear.
The main reason that I wonder about that is maybe because I've wandered on Modding Sites for too long. And I got my answer now:
On a Modding Forum, it's easier to pick a Mod based on what do they excel on (Sometimes you already know what do they excel on because you have already seen him/her in other Forum(s)). And most also fits for other roles such as watching the community. That makes Tryout System (nearly) completely obsolete.
However, on a Community Forum, it's harder to do because of the fact that you can't pick a Mod based on what they excel on (Except Game Development, ROM Hacking, and S&M). That's why Tryout System COULD work, but NOT always on these types of sites.
Feel free to ignore this.