There are several signs
This problem is somewhat the opposite, because in poker you are never sure of anything, your opponents can make a lot of traps, so in my opinion I would say that there is no clear sign of a bluff. Now my advice is not to bluff too much, and a good bluff is one where you don't run as much risk of losing a lot of chips or know that your opponent doesn't have much game, or you can also semi-bluff when you're close to making a game, I would say it's the best option