When people don't join our obviously far superior RP?

Foolish hubris and all that nonsense aside, we'd say that much of the above is relevant. Non-critical reviews by GMs is what we consider a major warning sign. Accepting Mary Sue characters is a bigger sign.

We're generally careful with reviews so we can be less strict IC. That let's us find the bad apples before they make too much of a mess. Overly impatient players tends to ring our warning bells. Eager players don't to the same degree, however.