The main difference between a service performed by the public sector and the same service performed by the private sector is that the latter must generate a profit.
That profit has 2 financial effects: it drives up prices or it drives down quality, which the purpose of either is to increase the profits generated. And sometimes both effects occur.
However, this doesn’t mean that the public sector isn’t immune to some of the same effects.
You see, the governments that want to privatize public services are the same governments that cut funding to remaining public services. And underfunding, like profit generation, drives down quality.
Take, for example, schools.
As austerity measures reduce public education funding, class sizes increase as a measure of accommodating a growing number of students with the same number of teachers. As the number of students per teacher increases, it reduces the amount of personalized attention the teacher can provide for students, which decreases the quality of education those students receive.
For another example, let’s say municipal governments pursue a 0% increase to the municipal property tax rate, even though their infrastructure keeps increasing and more people and businesses move into their city. That trickles down to less frequent lawn mowing, slower response times for road repairs, less reliable bus service, and so on.
But poor quality isn’t a result of it being a public service, despite what some politicians might tell you. It’s a result of deliberate underfunding, which itself is a result of poor tax policy, as a way to help the rich hoard more personal wealth.