them press on the third button from the top of the box (if it is a 10 button box) and push the bellows together.
If you have a piano handy, compare the accordion note to the piano notes. That 3rd button note on the push should be the key of that box. Could be out of tune, but will likely be between notes rather than shifted totally to another. What constitutes out of tune on a cajun box is for another topic.
Beats me why the manufacturers can't stamp, emboss or fix a plate to , say, the bottom, of the accordion with the "ex-factory" key..
It may also help a potential buyer to identify if an accordion has been retro-fitted with different keyed reeds ( perhaps dare I say inferior quality reeds ? )...ie. it plays like a Bb but it says it's a eg. Martin C ....
It may even be helpul if the embossing identified that it was a say, C box with eg. 5 c Wet tuning ex-factory.
ALL of the harmonica manufacturers have no problem with embossing their diatonic harps..why not discreet stamping/embossing on the accordions. ?
It's probably even better to force makers to use a CMA approved color scheme for accordions for each different key .... Like Cyan for C, Brown for B etc. Come to think of it, i'd love a totally Chrome plated Acadian for my C ..... Or a bar-code plus a free bar code reader? Two bleeps i C, three is D etc, so the blind will be less left in the dark .....
PS a converted accordion should be banned & branded with this sign across the bellows:
PS, maybe on the top i there's a nice crayfish present at the front ...