I've actually been surprised, more often than not, when I've found out how much people make (including some family friends I knew as a kid). It doesn't correlate all that well with how much I would've guessed they were making. One big reason is that people have wildly different savings rates, and I don't generally have a way to guess that: someone who "looks like" they're living at $70k/yr might actually be making a lot more and banking it for early retirement.
Another reason was that, even when only estimating spending, as a kid I tended to over-emphasize "conspicuous consumption" and gadgets: assumed the people with bigger TVs, new game consoles, better cars, etc. were wealthier. What I massively underestimated was the cost of "nice" vacations (esp. compared to relatively minor items like game consoles), so it was really the people who liked to travel a lot who spent more, but I never saw their spending happen when I was around.
edit: To add one more confound, I think I also put too much emphasis on "class" associations: I assumed parents working blue-collar jobs made less than white-collar, which was not always true, esp. when you took into account that some blue-collar families had 2x incomes.