Is a person sinful for using gold-plated tweezers to remove bothersome hair from his beard, despite his not being convinced by that due to its low price? And is expiation incumbent upon him?

The preponderant (most correct) opinion is that it is forbidden to use items plated with gold. Anyone who has done so must repent by increasing their righteous deeds, based on Allah’s Almighty saying: "But whoever repents after his wrongdoing and makes amends, Allah will surely accept his repentance. Indeed, Allah is Forgiving and Merciful." As for shaving the beard, it is forbidden due to the prohibition against shaving it and the command to let it grow and be abundant.