Having thought this is probably the best place to start, I'm putting out feelers to find the value of my Jeffries Duet - with a view to selling it... what I can tell you so far is:
How many buttons? 52 odd including the bypass(air intake thing)? and a bass note
Core or home key? wouldn't know one if it asked me out for dinner, what am I looking for and I'll let you know which it is
Condition, including Concert pitch? Very good nick, a couple of notes are a little squeeky (sticky?) - one of the straps will need repair / replacing - I have the original leather case, but it will need a new handle or repair to it.
Bellow airtightness? no puffing / wheezing or cracks etc. Bellows are sound to the best of my knowledge
Pad replacement? I've not put any in
Valve replacement? the metal things that are in a bag at the bottom of the case - several spares, it is as it was when my great grandfather passed away in the early / mid sixties, ever since stored in a wardrobe in dry conditions,
It needs maintenance as opposed to repair, I can try and send a video clip of playing (hah! can't play a note) the notes through to show you what good condition its in.
attached is a picture
I'll start again with a basic 'learner' at some stage, but the wife has said 'we' are learning the piano now...
Thanks
Rich