As Kidd mentioned, it is about trust.

There are very few people I allow to do non-bios on my thread. In fact, there are only like a handful of 5 people I would allow to do so, and only one has the preference to doing so. However, I have begun experimenting with an NPC->PC system in which people wanting to go the non-bio route, but are unsure of how they want to develop the character, are free to experiment with it IC. My only caveat is that if they engage in any combat they must first complete an acceptable bio.