Players nearly always believe the NPCs. As a corollary, when they do decide to distrust an NPC, it's nearly always the one they should be trustingIt leads to some very interesting developments, for sure, as an NPC can spout off nearly any sort of complete nonsense and the players will follow it right into a trap or worse. I'm not sure exactly what causes it but I suspect part of it is something I've also observed as a player:
GMs who never have their NPCs lieOnce a player comes to expect that NPCs will always be truthful, they're completely unprepared when they're not, and often skew the other direction by never trusting an NPC again.
It's possible that my experience is atypical and most GMs portray believable NPCs who don't exist only to infodump on the players. I mean, one of the most cliched pieces of advice ever for GMs is to give NPCs personality. Right? Right?
But just in case my experience is one of the more common, the article points out some great things about interactions with NPCs - namely, that NPCs who gossip and can use that relatively meaningless talk to make determinations about how much they trust the PC (or not). It doesn't mean that unimportant (or even important) NPCs should be full of all kinds of deep conversation. Quite the opposite, actually. Time to drag out those old rumor and gossip tables and let the NPCs just say some random shit mixed in with the crucial bits the PCs need to hear.