Thwy are a hit or miss. Ive had good as well as bad experiences with them. I did sell my series X to them last year, and it was fine. But i ensured to send videos and pics on email before packing, cause with discs they return a lot of them now claiming scratches , even when there are none.
Gamenation i feel might be better cause someone reaches out to you before pickup to check the condition etc on whatsapp call, but i think they offer a lower selling price.