Is my concertina leaking air? Help.

[Facupb]

I just recently received my first concertina, a Stagi 30 button. When I first tried it, I realized that it opened by itself more than what I would have hoped so. It plays in tune and has a great sound but, I find that a lot of air is required to play some notes, especially the lowest and the highest notes.
I have analyzed the bellow and it is undamaged. Is there a way for me to check if it is natural or if needs a repair?
I have noticed that when I stop playing and I am ready to compress it ( by pressing the air valve) to close it, it remains squeezed and then relaxes by letting air in, is this normal?
Here were I am from, the instrument is unheard of, should I contact an accordion luthier and ask for help?

Edited October 9, 2021 by Facupb

[Chris Ghent]

Squeeze the bellows without a button pressed and listen for leaks. Do the same with it held near your face (I put my tongue out because it is more sensitive) and you can feel small leaks. You have to do a lot of turning the concertina around because you will not feel a small leak unless you are within about 10mm 
 

The effect you are describing, does it occur when you have shut the bellows and then put the concertina down in a hard surface? Does the bellows then shuffle open on its own? If so, this is a fault condition, but if it is only a little you can live with it. If it is excessive it could be dealt with by taking the concertina apart and compressing the bellows in a clamp for the a fortnight. You need to make a couple of blocks to fit inside the entry to the bellows to get an even compression. A concertina repairer would be familiar with this process. Whether an accordion repairer would be I don’t know. 
 

But ask yourself, does it really get in the way, and is it worth getting it fixed on what is essentially a learner instrument?

[Theo]

My guess would be that on a new Stagi an air leak is more likely to be from a badly fitted pad, than from a defect in the bellows.  Listen for leaks as Chris has suggested, but also listen for leaks from each end.  A leaking pad is usually fairly easy to hear while closing the bellows, though not while opening.