But isn't it that no matter who you target and where, the click farms always steal the clicks?

Only if they have accounts inside those verticals. The more specific you are the less likely this is to be the case.

But aren't the click farms in every verticla, in every location?

No, there isn't any need for that. There will of course be some spread but it isn't intentional or planned. They don't need a solid distribution of verticals and locations for what they offer to clients since they don't need to see their clients ads just click like on their pages.