Saver Fares: These are really good, super-discounted deals (i.e. rare if you don't live along the Northeast Corridor (NEC)). They are non-refundable, but they will give you a voucher for that amount if you have to cancel. You can use that voucher toward a future trip. Think of these like last-minute airfare deals where seats are only $26. These fares are not available on all trains/buses.
Value Fares: If you cancel more than 24 hours in advance, it's fully refundable. If you cancel within 24 hours, there's a 10% refund fee. You can cancel and take the refund as a voucher if you want. These fares are available on all trains/buses.
Flexible Fares: Flexible Fares are 100% refundable without any refund fee. They can be canceled for a full refund of the ticket value or with the ticket value saved as a voucher. The Flexible Fare is available on most trains and buses. As such, these fares are a little bit higher because they don't have the refund fee.
Premium Service: These are your upgrades to business class and sleeper cars.
If you cancel a seat under Premium Service, the ticket is fully refundable as long as you cancel before the scheduled departure time. If you wait until after the departure time, a 10% fee applies.
If you cancel a room under Premium Service, you incur a 10% refund fee if it is 15 or more days before traveling. If canceled 14 days or fewer before the scheduled departure, you will not get a monetary refund, but they will give you a voucher.