Doesn't that already happen? And what evidence do you have to suggest that known income would make it worse on average? What about cases where a contractor would presume a client is wealthy and try to rip them off, but income data would show that they are actually not as well off as appearances suggest?

But I haven't really bothered to think through any of that, because my point was about kidnapping, which almost never happens in the US. Fewer than 100 people are kidnapped for ransom in the US every year.