In many contexts, aria fritta is a way of saying, "hot air," for example, when someone, such as a politician, goes on talking and talking without saying anything. It's "empty talk." In English, we have various ways of saying this, such as "Yada, yada, yada" (from the popular TV series "Seinfeld").
But in the context of a recent episode of Sposami, Nora is trying to sell what Iside, who is listening in, considers to be "fried air." In other words, she is making promises she won't be able to keep. Hype, but no substance. All talk and no action. You obviously can't fry air, so it is something with no substance, something that doesn't really exist.
Qui si vende aria fritta. -Ecco, esatto. Allora vengo subito lì e buttiamo giù l'accordo, va bene? -E il bello è che c'è qualcuno che se la compra [l'aria fritta].
Here we're selling fried air [empty promises]. -Right, exactly. So, I'll be right there, and we'll sketch out the agreement, all right? -And the good thing is that there is someone who buys it.
Captions 31-34, Sposami EP 4 - Part 23Play Caption
Nora is very good at what she does, and she might just pull off the deal she is making, and then it won't be aria fritta anymore.
Another expression using aria (air) to indicate nothingness: campato in aria (surviving on air, far-fetched, based on nothing).
Questa è tutta una sua ricostruzione totalmente campata in aria. -Campata in aria? Vuoi che ti dica le prove,
This is all her totally far-fetched reconstruction. -Far-fetched? You want me to tell you the evidence,Play Caption
Campato in aria is used as an adjective, whereas aria fritta is a noun. Aria fritta is given out intentionally, whereas campato in aria might just be an idea having no rational basis.