my personal rule is to only lay a trap that has clear potential to be discovered in-game, with a context clue, and not an ambiguous "roll for perception" out of nowhere.

randomly dropping an anvil on a player is a dick move.

telling players they're walking through an active construction site of a new smithing conglomerate, with an unfinished forge 10 meters above them, at least sets the tone and let's them know caution is a reasonable option.

also sets up some weird intrigue that could easily turn into a sidequest.

The confusion lies in calling them a GM. Sounds like they were just a dick