$1 billion transactions, 5% of that in fees, so $50 million in fees. Minus maybe $30 million in cost of payments (credit card transaction fees) which amazon eats, that only leaves maybe $20 million. Out of which amazon ends up having to handle a lot of bullshit like chargebacks, fraud issues, etc, which further erodes their profit down to a fraction of that $20 million.

Meanwhile, amazon.com retail earns probably $20 million an hour during the day, give or take.