Although there are many independent private bus companies in Brazil, all of them need to comply with public regulations. Your general rights as a passenger as enforced by these regulations include the following points:
When you cancel your bus trip at least three hours before departure you have the right to get a refund of at least 95 percent of the ticket price.
Your free baggage allowance is 30kg plus 5kg of hand baggage, and you have the right to get a receipt. In case of damages or loss you need to make your claim directly after arrival. The bus company is then obliged to pay compensation.
Any child under the age of six years without its own seat travels free of charge.
As a passenger you also need to respect some rather obvious obligations. You may be denied transport when you are drunk, can not proof your identity, or disturb other passengers. Smoking is not allowed, nor is the transport of dangerous items in your baggage.