Yeah, it’s not fair that kids will discover a strange problem that the adults will often overlook, and then the same adults just take over and pretend they care.
In the strip, CB actually says 10000 balls, not 10000 hits. I’m not sure whether it was a “garage salesman”, it could definitely be a tennis ball salesperson who said that.
At least she didn’t yell at Snoopy as hard as she did at the opponents.