I haven't finished my profile, just registered with the bare minimum without uploading the documents etc. so I could take a look around. But it seems that its just like getting an Uber cab with little or no PAX screening. I suppose you could get a nutter showing up, but then again that could happen at a flight school or even when taking a friend up if they had some mental or addiction issue that you were unaware of.
Thinking about it, if you were minded to top yourself by jumping out this would be a high profile (and cheap if you cancelled your card prior to take off) way of doing it if that's what you were after.