So you bought an accordion on EBAY and the seller forgot to mention that it has been sitting for years and it smells horribly when you open the case. I have had this happen many times and it is quite simple to de-smell the item but it does take time. I usually open the case and take it and the accordion to the garage and leave it sit there for about 2 weeks. Then I will go to an automotive supply or WalMart and but an auto deodorizer, especially one that is self adhesive and will stick to anything. Pick any flavor you think you like.  Cut the deodorizer in half. Take the accordion apart and insert one half somewhere on the treble side and the other half in the bass side. Now it will be important to play the accordion every day for a few minuets to deodorize the bellows..Ater about 4 weeks this thing will smell like a rose and you will be able to remove one of the deodorizers...the second one will come out later or may never need to come out...depending how is smells later on. This is the only method that I know works..