Hi, i've been using these for roughly 5 yrs and really love them. In all of my experiences, the wet side is where you want to look if you're buying preowned. Often times if they are pretty old or were used intensively, the magnet on the wetside can crack - i have had two in the past. i'd open the wetside and take a look immediately once you received them.
other than that, pairing is easy but youll have to do a hard reset - if it hasnt already. Then hit the "+" sign on the mobius app to add new device. make sure to update if you get the pop-up.
https://support.ecotechmarine.com/h...31098-VorTech-Propeller-Pump-Controller-Reset