Unless, you pay in to the IRS or have a refundable credit, you won't get a refund with self-employment. The only reason you have a refund as an employee is because your employer withholds tax and sends it to the IRS on a regular basis.
In your scenario, you pay receive $13. $10 is for the product and $3 is for shipping. You add both to income but you expense the $3 in shipping charges. In effect, it is added in but then subtracted, so it doesn't really count as income to you.
Paypal fees don't come into this equation. They are simply more expenses for you to deduct.
