In regards to the post about the Thieves guild, i feel like a small unsaid joke about them is that Vetinari pretty much turned them into tax collectors and people are happy to pay because they are somehow more ok with being robbed than they are with paying taxes even when the net result is exactly the same. It's not a big thing but it's a fun way to look at the Thieves guild and how people treat them.
It's true! Given that all the heads of the Guilds answer to Vetinari to some degree (although he lets them believe they're more independent than they are), the Thieves' Guild and all the others are in a way part of the Government. The Thieves are not only like specialized tax collectors (after all, they 'collect money with menaces' and Pratchett joked that's pretty much what taxation is), they're the local police force when it comes to unlicensed theft. Meanwhile the Assassins perform legal murder and come down hard on unlicensed assassination, and the Seamstresses have their own enforcers for violence against their members. Other Guilds require licenses to operate, too, and all of them collect dues. So basically, the Guilds work very nearly identically to government agencies, policing their own spheres and making their own money.
And yeah, it's VERY funny how the citizenry is happy to just pay protection money to the Thieves' Guild to make sure they only get a bit of a bump on the head during their one mugging per year, but they all HATE paying taxes to the point where Vetinari says that Ankh-Morpork, as a state, has little to no money in its coffers.