Regarding etiquette there are several maxims that should rigorously be adhered to. For example, in tournament play one should always be seated when their opponent is taking their turn at the table. Also, when a player is down on a shot at an adjacent table, one should take efforts not to walk past their sightline, as it can distract them from the shot.
However, "proper" etiquette can vary regionally, even within the same vicinity. In one pool hall in the city, opponents will snap their fingers in appreciation for a tough shot or well-executed kick or safety. Across town they will pound the butt of their cues on the floor. In the Chinese room even further they will tap their shafts on the rails for same.
In addition, around here less experienced players will say "good shot" towards their opponents with legitimate connotations. More advanced players are loath to do so. I've seen two pros in a big match bicker because one of them interjected a snarky "nice shot" after their opponent's turn, as amongst them it was construed as a shark (at their level).
However, "proper" etiquette can vary regionally, even within the same vicinity. In one pool hall in the city, opponents will snap their fingers in appreciation for a tough shot or well-executed kick or safety. Across town they will pound the butt of their cues on the floor. In the Chinese room even further they will tap their shafts on the rails for same.
In addition, around here less experienced players will say "good shot" towards their opponents with legitimate connotations. More advanced players are loath to do so. I've seen two pros in a big match bicker because one of them interjected a snarky "nice shot" after their opponent's turn, as amongst them it was construed as a shark (at their level).