Many tyre shops will have a preferred brand, some may be personal preference based upon experience, although others will have a financial incentive.
I buy quite a lot of tyres and generally split my business between the local tyre fitter and directly with Pirelli UK. I’ve used the local fitter for many years and will continue to do so because I like him and it’s handy having a fitter on the doorstep. Pirelli are incredible though, beautiful workshop, incredible technology and great facilities (eg tyre hotel).
However many years ago the local tyre fitter tried to get me to buy Hankooks but he was never too pushy and fitted what I wanted. I get on well with him though and he was honest enough to say that he gets an additional incentive when he sells Hankook tyres, but added that he genuinely rated them as tyres and knew that they were a great tyre for his average customer, ie those who don’t want rubbish, and don’t want to pay through the nose, hence choosing to favour Hankook tyres because he believed that they consistently offered good quality at a reasonable price.
That was many years ago and with the disruption of buying tyres online it may have changed this type of arrangement. If I remember right, a good indicator of where there’s an incentive in place was if the “branding” banners on the walls is pretty much all the same, as there were some “rules” to comply with. Surprise surprise my guy has Hankook everywhere except the inflation chart which always used to be Michelin!