Predict buying behavior under the condition that a customer is advertised or not
It depends what you want to do. If you want a model that will predict who to target/not-target for a marketing campaign, then you want to train a model using only the people who were marketed to, which defines your two classes "responders" and "nonresponders". Given an unseen customer, your classifier will then determine whether they are likely to respond if you send them a directed marketing advertisement. Take a look at uplift marketing.