eBay has seller fees.
Gumtree and Facebook Marketplace do not have any fees to sell.
eBay has a wider audience of potential buyers. Facebook Marketplace is gaining popularity as most people already have a Facebook account.
Here’s a recent Gumtree promotion for Australian’s:

Hello
We have a lot of stuff we would love you to sell.
Kayaks, bikes , trailer, furniture , artwork.
Would you be willing to come to us to have a look.
We are in Albert Park.