It is not a sign that something is wrong with a piece. It is not dirt. It is a chemical reaction between silver and sulphur compounds in the air, and it happens to all silver eventually. Antique silver in museums tarnishes. Your grandmother's teapot tarnished. It comes off.
What matters is knowing what speeds it up, and knowing which cleaning methods are safe for a piece that has a stone in it. Most of the damage we see on jewelry that comes back to us was not caused by wear. It was caused by cleaning.
