@Campbell
Your post about
trusting one another reminded me of my group's last Traveller session, which was earlier this year. A PC had been apprehended trying to break into a NPC noble's ship (don't ask!), and the noble was holding a trial of the PC - she believed herself to have the relevant authority to hold the trial, although the PCs on the planet didn't fully concede the point (don't ask!).
Anyway, the player of the PC first established that she still had all her gear. To which I answered
yes - nothing had been said about searching her or taking her stuff. And we confirmed that this included the grenade she was carrying. (It might even have been around this point that she used her psionic invisibility power to make sure the grenade wasn't detected.) And then the player confirmed that there would be a bit where she could say her piece - to which I answered yes, as that seemed to make sense for a trial. And we agreed that that would take place at the "front" of the space they were all in, with everyone else towards the "back" listening to the PC's oration. And then the player explained that, as she was saying her bit standing up the front, she pulled out her grenade and threw it into the crowd of everyone else - the noble NPC, her entourage, and another PC (a secondary character under a different player's control) who was siding with the noble against this PC.
The rest of the table was stunned. I assumed that the grenade was for making a daring escape by eg blowing open a hatch or something, not just blowing everyone up! The player of the secondary PC was outraged, not because of what happened to that PC - Bobby "the Robber" had had
dead meat (metaphorically) written on him since he first entered the campaign about 16 sessions earlier, so no one was very surprised or sad to see him go. It was the immorality of the action that shocked the player. A third player laughed at the audacity of it, and then had his PC who was in the vicinity, though not in the blast radius, help tidy up the evidence and finish off the survivors.
If and when the outraged player's main character - also a noble, who at the time of these events was on his ship in a different system - learns what happened, things could get ugly. Another possible source of ugliness may be when the PC who helped with the tidy up learns that the PC noble's NPC girlfriend/partner, who pilots his ship but is also a skilled physician, has been carrying out Alien-style medical experiments on the people put into her medical care, which happens to include the tidy-up PC's NPC girlfriend/friend-with-benefits. (Who came into that medical care as a result of being mauled by the result of the previous experiment on a NPC who had been one of the trial-holding noble's entourage but had been taken prisoner by the PCs.) Now that one is on me (the referee) as the initiator (though the taste for medical experimentation was well established before the NPC hooked up with the PC), but the player of the PC knows and the PC knows or at least very strongly suspects, but isn't doing anything about it because it's the PC's girlfriend/partner and she's the ship's pilot . . .
You kind-of just have to let the madness take its course and see what happens, don't you? It's no one's job to try and lock this stuff down.