The Eurail Pass

How can i get around paying extra charges when traveling by train through Italy with a Eurail pass?
I’ve read that when traveling through Italy you have to pay extra money to use trains even if you have a Eurail pass. Is there any way I can get around this? Haven’t I already paid for the train by paying for the Eurail pass?
Are these only certain companies that do this? If so, are there any companies that don’t?
It’s not just Italy. There are supplements or reservations fees required most places if you use the faster trains or night trains. The only way to avoid the fees if you use a Eurail pass is to take only the slower regional trains that take longer and may require train changes to go significant distances. The regional trains don’t require an extra fee.
Of course, you could always just buy individual point-to-point tickets and avoid the pass altogether. It’s often cheaper than the pass anyway – especially if you can buy tickets in advance and take advantag of discounts like the Amica fare on the higher speed trains here in Italy.
For trains that require a reservation/supplement, make sure you purchase it before you get on the train here in Italy. The additional fees & fines can be quite expensive.
Information on the supplemental fees is here: http://www.eurail.com/eurail-reservations-supplements-domestic , http://www.eurail.com/eurail-reservations-supplements-international-trains