On older boats, not unusual. Later models often have them. When my boat was 7 years old, a prior owner installed one. They are not expensive and fairly easy to install, might be something to consider if you should purchase a boat without an hour meter.I asked how many hours were on the engine but the owner did not know....apparently there is no instrument counting the hours?? Found that kinda odd....is that fairly normal?
Ask how much fuel the owner buys each year and how large a fuel tank he has. At cruising speed, he probably burns around .75 quarts per hour. From that you can get a rough estimate of the hours.