I have an HTC M8 for sale - very good condition (as in no visible scratches) since it lived in its case for all its life.

The battery must be dying because in the last few months it started turning itself off when reaching 25% or sometimes 10%. When that happened some settings would disappear (as in system options might reset, while installed apps would still be there). Something to do with the battery dying and not having time to flush cache, etc. 

Asking $50 for it - you can then replace battery, install a new ROM, do whatever you want...