I used to do trades on BGG and had great success both unloading games I was done with and picking up ones that I wanted. That was before shipping made that cost prohibitive.
These days I am on two local (Philadelphia area) Facebook game selling/trading groups where people post for local pick-ups. I am also on a local gaming discord group that has a channel for selling.
Finally, last year I went to an in-person board game swap that was great fun and I came home with some great stuff. Here is my description in another thread about that event: