The Internet is like a big city — a very big city. It has many nice neighborhoods with many good people, and it has a few bad neighborhoods with bad people.
As an eBay seller, you should try to be nice to everyone you encounter online, even if they are not nice to you. It may be difficult to avoid getting angry with a winning bidder who insists on using a payment method or a shipping method that you don't support (and have stated such in your sales policy). If the buyer has good feedback, you may be able to work out a compromise. For example, you could agree to accept his check, if he will agree to let you use one of your preferred shipping methods. Of course, the buyer's check will have to clear before the merchandise can be shipped.
No matter how hard you try, you won't make all of the people happy all of the time. You
When you encounter an angry buyer, do whatever is necessary to avoid negative feedback. Ask her what would fix the situation. Maybe she will settle for a partial refund and the merchandise. If she demands a full refund, including shipping, have her return the merchandise. Send the refund promptly. The one-time loss of $20 or $30 is a small price to pay for avoiding negative feedback that could hurt your sales for a long time.