I haven't found a better community for this question, so hope it's on-topic. I'm trying to understand how websites can profit from the personal data of the users. Everybody knows what they do in general, but the exact details are obscure to me, and probably to most other people as well. So to turn this question to something more appropriate for StackExchange, I'll ask it as if it was about my own website or app. Note that I don't intend to sell anybody's personal data or violate any privacy laws, it's just an example.
Suppose I have a website, or an app, where I can gather a lot of personal data. For example, think of an e-commerce (names, addresses, purchases, etc.) or a web forum (email addresses, interests, ad clicks, etc.). Now suppose I want to profit from this personal data. A large part of the internet seems to work based on such business models, where you get free services in exchange for... what? Nothing but your data. The question is: how do I do it exactly? I can only think of two ways:
So, can anybody tell me more about the possible methods and what exactly they involve?