[Propelloni]

Maybe you could build a heuristic around shipping weight? A single golf ball weighs about 45 to 50 g, so divide the shipping weight by, say, 50 g to account for boxing and so on and you get a rough estimate of the balls in the package.

[rockdiesel]

O wow, that's an interesting approach. That would've never crossed my mind without posting this on HN. Appreciate the suggestion.