Ok, this might seem a trivial question for some and it's not even a question, more like a discussion. I read the rules and I believe it's everything fine, so I'm gonna take my chances...
Here's the thing, I was thinking about how people build a dataset when they want to build a 'propensity to buy' model. For instance, I was checking some Kaggle notebooks, but it's hard to see them in the real world.
This dataset, for example, shows the visitors and buyers in a day. However, it doesn't look like something we would use in the real world, since it uses features like "the product was added to the shopping cart". I mean, unless the model is running 24/7, you won't have this information. And maybe you will get it only after is useful. Also, how would you use this model if it's running every second? These are just some of the things I'm confused, but this is not what I want to question right now.
This post, on the other hand, try to describe how to build a propensity model. It says the model will predict based on last purchases. But how would you build the training dataset? By only getting the purchases? Isn't this dataset biased? And if it's not only about getting the buyers? If not, when should you collect the data from other customers? For instance, if you work in Wallmart and want to know who is more prone to buy a TV, should you only consider the data from buyers? If not, the data being collected on November or December will result in different datasets, since the same person have different features depending on the date.
To summarize everything, let's think about a simple retail store. You have data from the last 5 years, data from all people who went there and bought something. You will release a new dishwasher next month. How would you build a model to predict which customers are going to buy this milk? Or even better, how would you build the training dataset for the task? Again, if you think about getting only the buyers, won't you miss potential customers? If not, is there any way of knowing which is the cutting point for the nonbuyers?