Arch wiki page on reflector states that:
Make sure the resulting /etc/pacman.d/mirrorlist does not contain entries that you consider untrustworthy before syncing or updating with pacman.
The question is, how should I know if a mirror is trustworthy or not?
Assuming you mean teach you how this is done? If so, it would appear that hooking into pacman is no longer the best way to do this (TBF, my Arch installs run for many years without reinstall so I’m not always up to date on best practices lol). Seems that setting up reflector as a systemd timer is now the preferred method.
https://wiki.archlinux.org/title/Reflector#pacman_hook
Right. I personaly run it as part of a script when I clean the pacman cache with the Scc options.
A note about this command: it deletes from the cache all past versions of installed packages and all uninstalled packages. This will prevent downgrading or reinstalling packages without downloading them again. One may prefer using less aggressive options or paccache.
Thanks!