Prices need to be made available online and prominently displayed at the entrance of the station. They shouldn't allow cheaper prices for subscriptions or even blocking any access without one.
Cheaper prices with subscriptions are not a problem at all. It's just that I should always see the final price that I will be paying per kWh before starting to charge.
On a related note, there is already a plug-and-charge system that identifies the car when it gets plugged in and is capable of charging the owner, but it almost never works. This is also something that should be mandated for larger EV adoption.
Subscriptions from major charging providers can easily run 15 Euros a month and for that you get electricity for up to 50% cheaper per kWh. There are also a lot of providers that you simply cannot charge with unless you are subscribed. Payment is only possible through their app or they send you a physical rfid token that's linked to your account.
In my town (200k inhabitants) roughly 40% of stations require you to sign up with the provider first before being able to use it.