Any definition of internet marketing needs to come along with a definition of things associated with it such as affiliate marketing, network marketing, multi-level marketing and so on and so forth. Some of these are less legitimate than others. For example, affiliate marketing is a tough nut to crack unless you have a massive following or you understand how to build excellent squeeze pages and effective sales funnels.
Just like a customer testimonial or product review can help to build trust in your company, your brand, and your product, they can also help to boost engagement. Watching someone demonstrate how your product or service improved their efficiency or solved their problem is so much more believable (and memorable) than just reading an article about it.