Buying tickets from the machine is really the most practical solution as many have noted. If you buy reserved seats there is a diagram of the seating and you can select how you sit. On the Eurostar trains the seats are not in compartments so you would find most are lined up facing one way. The trains with compartments, usually Intercity, are older and less comfortable. Once again, the best deals are usually on Regionales and these are the most flexible with no reservations at all. You just buy for the route and stamp the ticket before you get on the train. You can check out the prices and times on Trenitalia.com for Regionales as well as the fast trains. Sometimes only the Italian version of the site gives the prices for the Regionales. A trip from Venice to Florence has many opportunities for Regionale connections. When you have a reserved seat train, you have to wait even if it's seriously delayed. With Regionales, you can take whatever comes along. All the ones I used were air conditioned as well.