Well, that one didn't work out. Seller wants cash, and I'm OK with it, but told him I would not bring it first trip because if I didn't want the instrument I did not want to carry around that much money if I wasn't going to spend it. So he calls me a scammer.
But I'd still like some tips for buying used if anyone feels up to it.
Good move. Buying your first accordion used is difficult because you may not be able to recognize problems. And finding a good repair person is difficult. Best advice is to try to meet someone who knows about accordions that you can take with you to look at your purchase.
Otherwise, a couple things to check out include:
1. Overall appearance. Is it banged up, cracks, missing parts, smell (common), missing bellows tape, etc.
2. Sound. Does it just sound bad.... If you have a good ear, is it out of tune? Are some notes louder than others, or make funny noises.
3. Bellows compression. When you squeeze the bellows (gently please

) without notes pushed down, it should not not close easily. Relative, based on experience.
4. Condition of reeds, wax, and "leathers." If you can open the accordion (you should definitely try) check the condition of the reeds, there should be no corrosion, oxidation or rust. The wax should have no cracks or be totally dried out. The leathers should not be curled. Look for missing reeds or leathers. Note that it is normal not to have leathers on 4 or 5 highest pitched (smallest) reeds.
5. Air release valve should work.
6. Bass strap in good condition with adjustment to fit your hand. A lot harder to replace than shoulder straps.
7. Small parts in good shape - strap connections, feet, closing straps, etc.
Hope this helps.