I've received an order where the customer selected local pick up, thus avoiding shipping costs.
When they proceeded through paypal to make a payment paypal allowed them to enter a new delivery address, (which would incur shipping costs).
The issue with this particular customer will be easily rectified. However going forward is there any way of avoiding this potential scenario, where the customer can enter a new shipping address in paypal which may not match the shipping fee calculated.
The order placed with shopify will always superseded any changes in paypal, however, it does allow an opportunity for confusion and possibly disappointment with customers, who wont understand what's happening behind the scenes as they are asked for information through the check out process.