Every time I've looked into doing a trade-in they were only giving like 1/2 the market value of the phone, so I would just end up selling it using my fake account on facefuck marketplace locally.
I'd do fleabay as a last resort, because they take stupid fees now. Much better off selling it on fb or craigslist or another place without fees. I sold a phone last year on fleabay, look at the fees, 20%, $30 in taxes and fees on a $150 phone.
Yeah I've had problems with them too. I tried selling an older graphics card I had on there back when GPUs were harder to come by. I posted it with pictures and everything but like a few minutes after I listed it I was immediately banned with no way to appeal. Ended up just selling it on Craigslist instead for probably more then I would have made in the end with ebay.