Unfortunately the lucrative nature of such a model also means that it is ripe for the picking when it comes to scams, but the good news is that in Chrome 71, Google will have protective measures put into place where they will warn users against signing up for a subscription that they don’t know about.
For example there are some mobile websites that for whatever reason, require users to enter their phone number before proceeding. For more tech savvy ad seasoned internet users, this might already be something of a red flag, but there are probably plenty of users out there who might not be aware and will willingly provide their number, in which they could end up paying for a subscription to a service without knowing about it.
Now this isn’t to say that all such practices are deceptive, but if sites want to avoid being plastered with a warning like the screenshot to the right, they will need to follow Google’s practices which will require them to make billing information visible and obvious during the signup process to ensure that there is no confusion about what customers are signing up and paying for.