Just ging back to doctors recommending things or having brands:
A doctor that has a brand is clearly selling a product (and themselves). A good example is Marko Lens of Zelens - he has a big upmarket cosmetic surgery practice, naturally his clients ask him for products and he reasonably thinks he could have the cash instead of suggesting other people's products to them. So far, I'm fine with. I've never used Zelens but am prepared to believe they are very good products, going by the ingredients. However he's also upfront that he created the brand to be upmarket to sell to his rich clientele - there's a great video where he explains he doesn't give a stuff about parabens but his clientele are all convinced parabens are evil so he makdde sure not to put them in his products. And to sell an upmarket product you aren't going to price it at £5 a bottle, part of it being upmarket is that it's £££££. So I suspect Zelens is a great brand with great products but no way do they cost £££££ to make and market, a good wodge of what you are paying is pure profit.
Doctors recommending things is different and then I think you have to look at the context. Dr Sam Bunting has fronted various brands - a lot of the Mumsnet Q&A she did are clearly sponsored. She's also worked as the face of D&G beauty. It's up to you then to decide if you think the doctor is ethical enough to only join with good brands/products or not.
Other recommendations clearly come from their clinical experience - especially in dermatology you will be recommending things all the time. Every dermatologist in the UK prob recommends Cetaphil - because it's cheap, boring and nobody reacts to it. This isn't a commercial relationship. So they all probably have a collection of products they recommend over and over again and it's not surprising French pharmacy brands crop up here.
Finally they have products they will sell you if you go to their clinics - Dr Sam Bunting has often says she uses Obagi for example. Money will be changing hands here between them and the brand but given they are treating you for a problem, if the products don't work, you won't be happy! So although this is a commercial relationship, there's clinical skill being used too.