Not necessarily. A knowledge of marketing can help make rational consumers, but it does not guarantee that consumers will be rational.
If you have a knowledge of marketing, you are more likely to be a rational consumer. You should be able to see through some of the tricks that marketers use to induce you to buy things. This makes you more likely to make a good, rational decision to buy something (as opposed to an emotional decision based on what the marketing campaign made you feel).
However, not everyone with a knowledge of marketing will be able to do this. Some people may not be able to turn off their emotions and will respond to marketing campaigns even if, intellectually, they should know what is going on. Therefore, a knowledge of marketing does not necessarily make a rational consumer.