If it is a MG Wireless, it is either 45, 50(has been discontinued), or 55lb thrust, assuming it is a 12V version. There should be a "W" and number on the top of the head. The number cooresponds to the thrust.
Make sure shaft length fits your boat. Since he has a battery there, test it. The MG has a battery test function on it. Test turning right and left. Should be smooth in both directions. They can be a little noisy, but any grinding or binding is bad. Test the on/off and speed range. If any of the turn/speed don't work, do not assume a new foot or keyfob will fix it. It could be the control board, and it is rather expensive. Test the store and deploy. It should latch when stored.
New they go around $500. In excellent shape, like new, I'd start at $250.
Age: If it has a short black antenea, it is older. Newer ones have internal. If there is fadding in coloring it has sat in the sun allot. Look at the composite shaft. The cleaner and not scuffed it is, the less use it has had. If faded and shows allot of use, subtract $100.
No foot control: subtract $30.
Make sure the aluminum mounting plate is included. If not, about $35 new.
If including any wireless keyfobs add $25 each (about $50 new).
I wouldn't give much for a battery, unless it was load tested. so around $25, if it looks new.
FWIW: I bought a new W45-48" which included a free keyfob for $450, before other discounts. This was about 4 years ago.
I bought a used W45-52" w/foot control, no keyfob or mounting plate, showed some dis-color, but shaft showed little wear. I paid $100 without shipping. This was last winter.
Hopefully, that is enough for you to establish a price.
