OTOH, some of us know how to fit a bike because we've done tens of thousands of miles on a number of bikes. So there's that. But as DC mentioned, things vary. I think it's kind of like derailleur adjustment. If you don't know how to do it, it's going to be wrong a lot of the time.

Saddle height.
Saddle fore-and-aft position. Then readjust saddle height.
Bar height.
Reach to hoods.
Reach to drops.

Learn how to adjust these to get what you want and fix problems as they come up.