How do Muslims know which Hadiths to follow

[Minimalist]

The work of finding out if a hadith is relaible or not has basically all be already done for you by the so called Scholars of Islam.

Or, as H. L. Mencken noted....

Of learned men, the clergy show the lowest development of professional ethics. Any pastor is free to cadge customers from the divines of rival sects, and to denounce the divines themselves as theological quacks.
— H L Mencken,