Much depends on the size and shippability too. I use eBay for many items just because of the reach it has .. the downside being roughly 13% lost to fees. It's tough to sell physically large items there because of the cost to ship these days. I have sold items over $1000 many times through eBay .. some to all parts of the globe. I have sold speakers on eBay .. mostly listing them as local pickup only.
Other options for audio gear are reverb.com (low fees but less of an audience), Amazon (you can list used items there, but fees are slightly higher than eBay), Craigslist (good for local sales but high risks), and the newer ones like LetGo.
I have also listed items on the Facebook Marketplace (no charge) .. there are some specific to almost every genre.