Marketplace shipping and receiving?

Hey everyone, my name is Devin.
I am new to the IndieHacker community but have been working on projects for quite some time now. I would like to get more involved with you all and grow along side you.
One of my projects is based around a Facebook group I have. Members post items for sale and trade. I have created an (off Facebook) marketplace so members can take control over their sales.
A question I’m struggling with rn is, what would be the best way to handle sales for items not yet delivered? Obviously sites like Amazon and eBay have the credibility and insurance options to back purchases. How can I intermediate the exchange of money for goods that may or may not be delivered?
I’m open to all suggestions!
Thanks everyone!