Which individuals and businesses have something to gain from what the public believes?
Think along the lines of public opinion and the institutions and businesses that are influenced by public opinion.
All businesses want to have a positive public image, but the main trick is simply to avoid having a negative one. When a company has a bad reputation for its products, how it treats its employees, or for public and consumer safety, this hurts business, plain and simple. After the BP oil spill in the Gulf in 2010, a fair number of Americans simply refused to buy oil from BP gas stations for a time, as a consumer protest against how badly that whole thing was handled. This is why those slick ad campaigns come out after scandals, to rebrand the company's image into something favorable again, counting on the fact that Americans tend to have short memories.
It is true that determining public opinion is a big business. For example, advertising rates are set by who supposedly does and does not watch certain programming on television. Politicians commission expensive polls to determine public opinion and publicists to shape it. Therefore finding and creating public opinion is indeed a big business, even though human behavior can often be interpreted, influenced and predicted, there are times when people are extremely difficult to predict.
First, there are businesses that make their money figuring out what the public believes. For example, market research firms help businesses shape their products to fit what the public wants.
Second, some benefit from government actions that respond to particular public concerns. Note that this includes both those who are the natural beneficiaries of policies and those who are in a position to take advantage of public opinion to twist things to their own ends.
For example, if the public believes that government is taking too much from the people, then it is easier to pass tax cuts. The natural beneficiaries of that are all the people who pay taxes. The corrupt beneficiaries are those who manage to use the momentum of public opinion to slip in special tax benefits for them.
Another example is if the public is convinced that military action is needed to protect national security, the natural beneficiaries are the various companies that manufacture related products, such as weapons, uniforms, surveillance systems, etc. The corrupt beneficiaries are those who take advantage of the situation. For example, right after Saddam Hussein was toppled we sent a huge flow of money to Iraq. Many contractors were able to take advantage of that to overcharge and even siphon off money.