In early July, I will be traveling from Rome to Florence for a day trip. Am I okay purchasing train tickets when I get to the station or is it better to buy them in advance online?
Purchase at the station, as there are multiple trips per day and they are very rarely full. I would only recommend that you purchase in advance if you are traveling as a large group and you all wish to sit together.
If you are at all worried, just stop by any train station (or even any travel agent in Rome) once you are there to purchase your ticket to/from Florence a few days in advance. Despite that, I would not worry at all so long as you can be flexible and wait an hour for the next train if need be.
By the way, you probably want to consider using an automated ticket machine at the stations as the lineups for the ticket agents can be massive - especially at Firenze SMN station (Florence Santa Maria Novella - the main station in Florence). For steps on how to use the automated machines, read this excellent guide from Ron in Rome.
Steven,
Thank you so much for your reply. The links you sent are very helpful and I will now purchase my roundtrip ticket just a day or two in advance.
Diane
My pleasure Diane - have a great trip!