1/ what do you mean by “Alpha SSL” ?
2/ your seller is only accepting encrypted payment. You should se up your magento in the way where you have certificats added, and ready t be use.
Paypal IPN is available but there seems to be no options where to add certificats. One of my seller accept only encrypted communication to his paypal account also. I’m interested into this feature also.
Paypal Direct is only available for UK and US people, meaning all other merchants that are using paypal can only use unencrypted Paypal IPN module which is inside magento.
Maybe we should look at creating our own paypal module.
let me know your thoughts.