I tend to agree with a few others here, Quality is not just the absence of problems, it is something deeper.

For me it means care and attention were paid while developing, the rough edges have been smoothed off for want of a better phrase. This doesn't mean using the latest and greatest framework or library, usually quality will come from a deep understanding of the basics and concepts like design patterns .

You can spot quality code in the same way to can tell a fake Rolex from a real one but the quality of the movement.