Safest way to sell/ship something?

I am selling something on Facebook marketplace and someone out of state wants me to ship it to them. I have never done this before. How do I make sure I get the money and they don't cancel the payment after I ship it? I'm selling the item for $150, so I want to make sure I don't get scammed. I usually would not consider this, but this is the only person who has showed interest and I need to sell it asap.