Researchers recruited participants for a wine tasting study that included a variety of wines in terms of style and price. The participants tasted a series of wines in a random order. Participants could look at the bottle for each wine so they could take its price and label information into account as they tasted and rated each wine. The participants rated the more expensive wines significantly better tasting than the less expensive wines. The researchers carrying out the study conclude that more expensive wines taste better.

Required:
What is a confounding variable that makes their conclusion inappropriate?