I'm close to Larry on this one. Lack of brand exposure and age are against you. I'm guessing $1,000 to $1,200.
If you are located where the buyer can play the instrument, you could add another $150 if the box measures up.
It's risky buying an accordion in the dark, thus buyers are stingy without hands-on playing. As-is long distance sales can be difficult for both parties.
You've gotten some good advice. Gonna be real hard to get a value on an older accordion made by someone few know, especially without pictures. I recommend getting some good pictures, including close ups of the keyboard and the inside. Seeing the workmanship and the type of reeds will go a long way. Knowing the reeds are made in Italy does very little for Cajun music fans, but the exact brand may help desirability a lot.
But in the end, as was mentioned, any accordion made by any one other than a well know builder, will have a lot of understandable reservation among buyers who can't play it.