Very.
There are some obvious red flags, like password protected archive and the dev asking you on discord to try his game, or the game asking for admin rights. The last one is not only against potential malware, but against amateur devs screwing with your system installation.
It helps if the game is a few months old, has lots of ratings and an active community. Most dubious games you will find in the most recent browse section. But also in new & popular. But some malware is put onto hacked accounts.