My 2006 Brera 2.4 was very well built indeed, and my current 2008 159 Ti is similarly well screwed together. No complaints with build quality on either car.
Although as a consumer I share your aspiration to experience no issues with a car, I am not sure that expecting this in a used car is realistic. Each individual experience differs, of course, but I've never, ever, driven a used car (even a low mileage one) with which I couldn't identify one issue or another that one could find annoying.
Even some of the new cars I've test-driven have exhibited little squeaks or rattles.
Overall, all of the new-generation Alfas are a massive leap forward and, in my personal experience only, easily match the build quality of the so-called "prestige" rivals.
The main thing, however, is to be sure that you are personally happy with any car. Each person's perception, expectations and "hot buttons" will differ.