You could sell it on ebay however to determine its value you will have to have a professional examine it. Are the reeds in tune; is the wax still soft; is there rust on the reeds; is there a mildew odor; is the bellows in good shape; are all the keys level; are the felt pads still good; are the leathers supple; is it mechanically solid; are the straps good;, what kind of reeds are in it - factory, hand finished, or hand made; did the last guy who tuned it know what he was doing; how many reed banks are there, how many shifts, how many keys/buttons. The answers to all of these questions will affect its value tremendously. Tuning a full size instrument can cost upwards of $400. New pads and felts could add another $150 or so, new bellows $400. If it smells mildew then it is probally junk. Being rare does not make an accordion valuable. Being old does not make it valuable. Quality, condition and sound make it valuable. The exception being if there is something special about who it belonged to or who manufactored it or if there is something special about the design. Old accordions generally do not become antiques - just old worn out instruments. People are often shocked to find out that it will cost seven or eight hundred dollars to restore their prize and that it wil then be worth only $400. Your accordion could be worth anything between $50 and $2000. The only way you will know is to take it to an accordion repairman and have him look inside and play it. Anyone who says they can tell from looking at the outside is an idiot. Most accordion repair places will charge you $20 to $50 for an evaluation. Most music stores will not have a clue. There are over a thousand pieces in a full size accordion - as many parts as in a grand piano. Check and see if you have a local accordion club. Often a repair person will belong to the club or one of the members has enough experience to provide a good evaluation or someone will want to acquire another accordion. If you sell it on ebay make sure you take pictures of everything - inside and out. If I might make a suggestion - learn to play it. That will be your best investment.
Good luck