I see a lot of gear being sold through photography communities on Facebook/Instagram. I think it make sense to do it through a community of photographers, especially where people actually know each other and their reputations within the community will keep them honest.
If I were buying an expensive used lens, I'd want to inspect it in person before handing over my money. There's only so much you can tell from photos, and going through the dispute process can be a pain for everyone. Selling locally to someone you can meet with in person seems like the best way to go, if you're in an area with plenty of potential buyers. That way there's no question about the condition of the gear at time of sale.