There are two main types of such search engines. The first type is one that combines multiple search engines; this is called a meta search engine. Examples of meta search engines are:...
They sell advertising not just space but also promotion techniques. They are also paid when they put a client's product at or near the top of a search result. Even a small amount of money for each...
I had a similar problem and tried for months to sort it out. In the end I used a company to help. They are called ClydeStan. http://www.clydestan.com There is lots of info on their site how they do...