Wouldn't trade in my phone

Devices traded in are usually reconditioned and used to replace other devices that were lost or damaged for insurance claims.  A s8 is well beyond the threshold for devices that people would be using today.  T-Mobile's network has changed a lot since the days of the s8's.  You will always get more money selling your device on something like Swappa, Ebay, or by giving it to someone you know that can make use of it.  There are promos out there that don't require a trade-in and don't have to be for the latest and greatest flagship.  The Go50 Plus plan offers current customers the same deals as new customers when it comes to upgrading.