I'm baffled by how wiggle/CRC are in trouble. I thought that they were a big online only retailer with minimal costs as they don't have bricks and mortar stores to manage.
You might have a smaller geographic radius on fb as it's collection only, but (in my experience anyway) the amount of people that view/show interest is higher on FB marketplace due to the much higher volume of users.
Plus it's free so nothing to lose by trying it.
I think you're using it wrong. Write your advert, set your price and that's it.
No postage, cash on collection only.
Same with Gumtree.
Never agree to post any item, it's not set up for that.