In late 1700s France, the government did a lot of things to avoid rudely asking exactly how much money someone made:
For instance, the contribution sur les portes etfinétres, or “doors and windows tax,” was based on the number of doors and windows in the taxpayer’s principal residence, an index of wealth that, from the taxpayer’s point of view, had the great merit of allowing the tax collector to determine the amount due without entering the taxpayer’s home, much less peering into his account books.
From Piketty.