Does Karl Marx believe the relationship between the two classes are friendly?

No, he didn't

Explanation:

Marx believed that the relationship between the lower class and upper class were exclusively beneficial for the upper class.

According to his perspective, Upper class owned the resources and employed the labors from the lower class. The profit that generated from that labor mostly will obtained by the upper class while the lower class obtain very little from it. On top of that, the sales of the product that created by the effort were mostly bought by the lower class citizens and trapped them in never ending cycle.

in this scenario it would be the consumer demand as most influential in making the decision. the band members need to figure out where and from whom they will make the most money, in other words who out of the two consumer groups - football fans or car drivers - will spend their money, who is more likely to contribute to their cause and buy what they are offering.