It's not true that doctors can't advertise, there are just restrictions of the type of advertisement they can do. There are e.g. many online portals that list d

It's not true that doctors can't advertise, there are just restrictions of the type of advertisement they can do. There are e.g. many online portals that list doctors with their specific services and contain appraisals by customers. It would just not be allowed for the doctor to do such kind of appraisals ("I'm the greatest dentist in Berlin") by themselves. In any case it's hardly an issue for them as most doctors are fully booked for months, so they rarely need to advertise their services. Companies like Doctolib therefore aim more at optimizing the booking process to e.g. ensure that canceled bookings get backfilled automatically to increase the overall booking rate, though even that is usually not a problem and most doctors overbook their appointments to make sure they stay busy during the day (that's why you often have to wait 30-60 minutes here even if you have an appointment scheduled).