All the previous answers seem legitimate, except the question itself is rather curious to me: however I will still attempt to clarify your doubts.
No jail, no 1000 euros, no court, no SIS, no ECHR (which was made to protect those who owe tens of thousands, not for a 30 euro bus fine), no prison. If you really can’t find peace, then give a call to ATAF instead of asking here.
Normally when you get fined for fare evasion the fine is an administrative one. So they will send you a bill to your home address, and if you do not pay, a reminder.
If you do not do that they may, or may not, decide to take this to court. Some countries take this more seriously than others. (In Switzerland for example they will not just drop this). If you do not appear on your day in court then they will make in entry in the Schengen Information System, and you will be in trouble the next time you enter Europe (not just Italy).
Being detained at the border for an outstanding fine does actually happen. It is what the Schengen Information System is there for.
The European Convention on Human Rights in 1950 banned debtors prisons. The border guard is not dealing with traffic fines. Chasing a minor fine like this internationally is simply not worth attorney’s fees. You are good to go.
Credit:stackoverflow.com‘