When he's talking his way into a crime scene or whatever, his believability is only so-so, and he's even worse when he's lying about something he cares about

That's very true, but part of my thinking was that since he lies (well or not) so often, I would expect him to expect to be lied to frequently, too- so I would expect him to automatically distrust people and keep them at a distance. If he didn't lie to Bela, I would have thought he might just refuse to answer unless she gave him a really convincing reason; he's good at blowing people off.