Personally, I agree with SlowwHand, and will take that farther. Adam Smith's is a luxury, and should not guide your construction decisions.
If you wish to grow under a republic or democracy, a marketplace is a necessity. A library is not. As a general rule, it is much more important for a city to grow, rather than languish in squalor even with something like a shining new library. Often, esp. at higher difficulty levels in a large empire, a marketplace is essential for WLT_ days, regardless of what the coin situation is.
If you are in a sprawling monarchy with say, about 40 advances, most cities will not need marketplaces (high corruption, and I always set 0% lux). Cities in your inner core might produce enough coin to justify a marketplace, but they can still generally wait.
In Republic/Democracy (deity), marketplaces are a given, and banks will be essential for growth sometime after size 12, assuming you have 30% luxuries set.
Since I try to RB/PRB almost all city improvements from mid-game onwards (help fund with caravan/freight), the sooner a city has an economic improvement, the sooner it is earning a return. More subtly, it will free up production for the (expensive to RB/PRB) units like freight & spies.
If you switch to Fundamentalism and have Mich. Chapel & JS Bach, you should probably rush-buy almost all your marketplaces when your new city is still size 1. In Fundy, my cities get libraries only after all the economic improvements.