The key limitation of using this sample to predict the preferences of the entire population of organic product consumers is:
B. The sample is limited to a specific demographic of consumers who shop at upscale stores, which may not represent the general population of organic product consumers.
This option highlights that the sample drawn is from a specific group of consumers (those shopping at upscale stores) which may lead to bias in understanding the preferences of the broader population of organic product consumers, who may have different shopping habits and preferences.