The guy at the store filmed my running, pointed out that (according to him) my feet bend inwards when running and recommended some Adidas shoes that (again, according to him) would "fix" the bending and make it fully vertical. I got instead terrible knee pain, to the point of barely being able to go up the stairs.
The second doctor told me to rip the insoles and replace them with some orthopedic, custom-made ones (my insurance covers a pair or two a year) and also prescribed me some knee pads with metal rods on the sides that I must wear whenever I run. He also sent me to physiotherapy for a month where I learned exercises to strengthen the knee and core muscles. Whenever my knees start to hurt (typically after not exercising for a while) these exercises make it go away.