Doesn't Google prevent invalid clicks?

Partly. Google filters some invalid clicks and does not charge you for them. For invalid clicks you were charged for, you file a claim, and any credit arrives after the budget is spent. Google's rules are the same for every advertiser.

Tapper works in your ad account. When it flags a click, it excludes the source so it stops seeing your ads, and the rules are yours: you set how many clicks from one IP count as invalid. See Doesn't Google already filter invalid clicks?.