A: [Surprising fact]
When someone has a claim questioned, there are two common responses. One is to treat the question as a challenge, intended as an insult or indicating a lack of trust. If you have this model of interaction you think people should take your word for things, and feel hurt when they don't. Another response is to treat the question as a signal of respect: they take what you're saying seriously and are trying to integrate it into their understanding of the world. If you have this model of interaction then it's the people who smile, nod, and give no indication of their disagreement that are being disrespectful.
Within either of these groups you can just follow the social norm, but it's harder across groups. Recently I was talking to a friend who claimed that in their state income taxes per dollar went down as you earned more. This struck me as really surprising and kind of unlikely: usually it goes the other way around.  I'm very much in the latter group described above, while I was pretty sure my friend was in the former. Even though I suspected they would treat it as disrespectful if I asked for details and tried to confirm their claim, it would have felt much more disrespectful for me to just pretend to accept it and move on. What do you do in situations like this?
(Especially given that I think the "disagreement as respect" version builds healthier communities...)
 Our tax system does have regressive components, where poor people sometimes pay a higher percentage of their income as tax than richer people, but it's things like high taxes on cigarettes (which rich people don't consume as much), sales taxes (rich people spend less of their income), and a lower capital gains tax rate (poorer people earn way less in capital gains). I tried to clarify to see if this is what my friend meant, but they were clear that they were talking about "report your income to the state, get charged a higher percentage as tax if your income is lower".
I also posted this on my blog.