Who pays whom: premium, credit and debit

You sold a call this morning for $300. Is that $300 income you have earned today?

• Yes; the premium is yours whatever happens, so it's earned
• No; you keep it, but it's the price of an obligation that is still open and may cost more
• No; it is refunded to the buyer if the call expires

A package is opened for a net credit. What does that tell you?

• The trade is lower risk than a debit trade
• The most you can lose is the credit
• Only that more premium came in than went out at entry