I just purchased this game the other day and after playing a few dozen games in a row (yes, I am addicted already) I thought of a rule variant for the Tax Collector. As reported by others, his ability can seem somewhat wasted in many cases because upon being revealed, players are more likely to spend their hard earned gold before paying the tax.
The power of the Tax Collector, in my opinion, is that he basically forces people to spend all their money building whatever they can afford, rather than saving up for something expensive. If you're already leading the game, taking the tax collector can be a good way to keep everyone else down. Also, if an opponent you're worried about seems to have a sizable amount of gold but hasn't built anything, there's a good chance they won't be able to get rid of it all anyway, and you can skim some gold from them while potentially making them waste money they had earmarked for something else.
Whether you get money out of people or just force them to build before they're ready (or to withhold building when they ARE ready), the tax collector is seldom wasted. Both results can be tactically beneficial to you if you pick him at the right time.
Wouldn't it be a more strategic character role if the tax collector collected the tax prior to a player building a district in his city? He would then become quite a powerful choice because his ability would work twofold in the sense that not only could he collect money from other players but he could also serve to inhibit other players from building if they were low on cash or had just enough to build a district.
I don't see this house rule breaking anything major in the game. Go ahead and give it a spin. Let us know how it works out for you.
From a logical angle this rule would make sense as one cannot build or buy property without paying taxes in a real world setting. Likewise, shouldn't this be the case in a fantasy world as well?
Actually, taxes are generally collected after the fact, based on how much income/property/whatever you currently own and claim on tax reports. There are certainly a number of expenses involved in constructing a building (or an entire district!) that need to be paid up front, but taxes are not one of them.
Of course, in the REAL world, failing to pay your taxes because you don't have any money left wouldn't exactly get you out of your debt. =P
Also, I'm sure there are some who would argue the entire point of a fantasy world is to escape reality. =)