> I asked them what sample attribute had the highest correlation with sales and without even hesitating they told me it was sugar content.

This was the cause of a big scandal back in the 1980s when it was discovered that some Austrian winemakers were adding antifreeze to their wines. The wines are tested for their sugar content, but diethylene glycol has a sweet test and wouldn't be detected on standard chemical tests for sugar. Unscrupulous winemakers began adding the chemical to their wines to make them taste sweeter and boost sales.