Way in eBay / PayPal to get a list of all email addresses of people you have previously sold to

The only method I know is to sell so many items that the negative feedback is drowned out by the positive. I've seen this effect looking at some high-volume sellers that sell over a hundred items per day.

If you refunded the payment, rather than cancelling it, the fees are also refunded provided the payment was for goods or services.

You can partially or fully refund a buyer within 60 days of receiving their payment. Refunds are available only for transactions involving the purchase of goods and services.

When issuing a full refund, your original transaction fee is credited to you. When issuing a partial refund, a portion of the fee is credited to you.

Source: PayPal