Which Appliance Manufacturers have their own in house repair technicians?

I know BSH group (Bosch, Siemens, Neff, Gaggenau) do and Miele do? Do the likes of LG, Samsung, Electrolux, Whirlpool/Hotpoint, Beko etc outsource to Domestic & General and the likes of Service Power? I’m asking because I’m having an air damper replaced on my Siemens Fridge Freezer. And dealing with BSH is okay. Whereas I have been reading the reviews of the LG and Samsung Appliances companies on TrustPilot and Consumer Reports etc and the reviews are generally horrific. Which makes me question if I can trust Which? reviews anymore. Because these days the highest rated Fridge Freezers are always LG and Samsung models and the same with Washing Machines.