1. If you select Pay Later and click NEXT, then the registration is over. So at that point it is too late to change your payment option. When registration is completed, the session dies which is why the amount is 0. However, there is nothing to change here. We can not disable the browser\'s back button
2. Again, you\'re talking about the use of the browser\'s back button. This is never a good idea to use in any type of form situation... especially when going back and forth between two different sites. Once you move to paypal, the data goes to a separate database table for paypal session data. Then if the payment is made, the registration record is created from that data.
My only suggestion here would be to modify the language file to change the text that shows above the payment type options... tell people to NOT use the browser\'s back button and that once they choose a payment type, if they change their mind, they\'ll need to start the process over.
This may seem harsh, but since you\'re sending people to another website, your session is lost. Sessions and browser back buttons don\'t play nice together.