Suppose you have heard about hypnosis from a friend. You want to try this out as well. The best thing first is to make some search on either internet or make some inquiries from the companies providing DVDs.  The more search you conduct on the internet, you will find out certain ways of how people have responded to hypnotherapy exercise and instructors. Just buying the product without any initial knowledge would be dangerous. You simply check out the web posts and user comments about the products that they have posted after using the free audio or DVDs. You will be able to judge very quickly how people have learnt hypnosis. 

Companies do ask for a post purchase survey or a customer feed back after selling the product. You can interview those who have used the product and would be able to make a judgment of the problems they faced. 

If self-hypnosis is concerned, you can do the same. You can make an online survey and ask those who were comfortable with the product. Those having problems with the product, you can ask them to leave some comments or provide a lengthy feed back on the product. Famous companies do follow a long term strategy. They go for product improvements after getting the customer feed back. They either make changes in the declining stage or at the maturity stage. The product needs some adaptability in the maturity stage. Firms do need to make an analysis of what stage they are into.