1. Some customers might be unhappy but didn’t complain.
2. The fact that few customers complain when they are given margarine might be explained by other factors, not necessarily by the explanations provided by the author.
3. The author fails to indicate the actual number of servers who reported, and what percentage of the whole server group do they make up, thus we cannot evaluate if the fact cited above is significant. Also, the author does not tell us the percentage of customers who do not complain.