I have the following, pretty standard, flow from product selection through to payment:
1. Customer adds a product to cart
2. Customer views cart
3. Customer selects ‘Checkout’
4. Customer enters shipping address
5. Shipping fee is calculated
6. Customer views full costs selects ‘pay now’
7. Cart item, and shipping details are sent to PayPal
8. Customer logs into Paypal, views purchase details and authorises payment
9. Customer returns to site

I’m wondering what security issues I should be considering, the payment is PayPal’s responsibility, and I’m not storing any customer details apart from sale tokens/details, but:
Is there anything should I be double checking?
What if a customer enters a shipping address that is different to the one they have stored at Paypal, are there any issues regarding Paypal seller guarentees, should I only send to the Paypal stored address?