It happens all the time at any level, but especially the pro tours where most people generally hit it the same number (someone might be a club long or a club short, but very rarely is anyone 2 on either side). Usually, though, you just look in the bag without touching. Some players ask what floor their room in the hotel is at or how many apples they pick up at once or something, which I like less. I'm surprised these caddies would be so blatantly obvious. The above is not cheating (mostly the first, the second is for sure questionable), but what Koepka's caddie did is clearly in violation of the rules of golf