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Have you ever offered your children or nephews or other youngsters being paid for a necessary service for you? There are thousands of variants like walking your dog, bringing newspapers, shoveling away snow from your porch.
The scheme is simple: necessary action was made, you gave money for it.
If the situation seems to be familiar to you, it means you have already implemented CPA model into real life.
It works the same in an advertising world: the ads owner pays each time when users performed an action he was interested in, it may be downloading a plan of future event, subscription to a newsletter, leaving an e-mail for a discount etc. People obtain the information or other benefits, while the other party gets a database of potential clients. It should be thoroughly examined to make stable partnership and get loyal customers.
Main advantage of this model is that you have a high quality of traffic. The users who made the actions you asked are much more likely to be interested in your products or services.
CPA model is often used in banner advertising now. There is no need to install complicated software on your website to track the process of an ad campaign, there are CPA networks that will make all the staff for you.