Tihiy

Bullshit. Nobody ever wants to talk with another human being and line up to touch kiosks. You contact far more pathogens by touching public handrails and doorknobs.

Yep that's just as awful as JavaScript.

I mean something like PayPal IPN or another system which notifies my server about a purchase so I can send digital good to buyer e-mail for example.

Excellent idea! Waiting for digital goods selling / purchase notification API.

But.. if you give money to sellers with PayPal, you're paying PayPal fee?