We did establish that finding unexpected blueberries at a farmer's market would be considered a good thing

Is that because they're blueberries, or because they're unexpected? It may be that the surprise of unexpected blueberries is bad, but the blueberries themselves are good, so that "expected blueberries" > "unexpected blueberries" > "expected lack of blueberries" > "unexpected lack of blueberries".