It doesn’t matter how often the possum would have scratched it. If your tent would be scratched 50% of the time in the absence of a bear, and a bear would scratch it 20% of the time, then the chance it gets scratched if there is a bear is 1-(1-50%)(1-20%), or 60%. Unless you’re postulating that bears always scare off anything else that might scratch the tent.
Also, what about how some of these probabilities are entangled with each other? Your tent being flipped over will almost always involve your tent being scratched, so once we condition on the tent being flipped over, that screens off the evidence from the tent being scratched.
Also, only 95% chance a bear would look like a bear? And only 0.01% chance it would eat you?
Realistically, once we’ve seen a bear-shaped object scratch your tent, flip it over, and start eating you, you should be way more confident than 38 to 1 that you’re being eaten.
Because I want to keep the option of being able to make promises. This way, people can trust that, while I might not answer every question they ask, the things that I do say to them are the truth. If I sometimes lie to them, that’s no longer the case, and I’m no longer able to trustworthily communicate at all.
Meta-honesty is an alternate proposed policy that could perhaps reduce some of the complication, but I think it only adds new complication because people have to ask you questions on the meta level whenever you say something for which they might suspect a lie. That being said, I also do stick to meta-honesty rules, and am always willing to discuss why I’m Glomarizing about something or my general policies about lying.