Can you sell your stuff online?
That may be like asking, "May I sell my stuff online?" And I give your permission and say "Yes!"
What you're probably more likely asking is, "How do I sell my stuff online?" And to this, I'd say, using the Habit Change LAB and positioning yourself to sell stuff online...as a short answer.
Now, let me dive a bit deeper into the 'How to do it' part...