When you purchase an antique accordion, don't forget to check the condition of the carrying case. Look for broken or missing hardware as possible. Note that a musty smelling case or bellows is one of the many indications that the accordion or other instrument may have been improperly cared for and stored, probably in damp basement. A musty case may also cause damage to the wood and leathers in the interior of the instrument. With this, its not impossible that the reeds may be rusted.
Check the Body of the Instrument
When we say antique, we are referring to something old, thus a certain defect is possible, unless the thing is really properly cared for. So, in terms of buying an antique accordion, looking for chips missing from the corners, cracks in the celluloid, scratch marks indicating abuse, and others is a pretty nice move to take. If possible, check the condition of all the leather straps, especially the ends that go through the metal holding brackets on the accordion, both top and bottom. If you find that the straps are much worn, then I think it is safer if you remove them entirely than risk their breaking while you are wearing the antique accordion.
Eyeball the Bellows
When you consider buying an antique accordion, try looking for signs of wear, especially on the folds at the base, as well as on the belt buckle wear (facing the chest of the player). Aside from this, check the corners of the bellows and look for corners that are missing or coming loose. Also make sure that in an antique accordion, all the bellows pins are still present and they are not folded or frozen in place with rust. Also note that in a piano accordion, for instance, the air release button is found poking through the bass cover at the left hand side towards the top of the instrument when held in playing position. So, if your antique accordion doesnt have one, then this is a serious design flaw.
Look at the Keyboard
When checking the antique accordion, try looking at the keyboard edge on, especially the white keys. Note that a properly labeled keyboard is unusual in a very old instrument, unless it has been well cared for. So, check for keys that are out of level as the irregularity of the keys will impede performance in general.
Play It Yourself
It is often said that the best to check the performance of an instrument is to play it yourself. Try listening for the intonation, overall tone, dynamic range, volume, balance between the left and right sides, and the action of the antique accordion. Or, let another person play it, and listen to the sound.