This would be a potential use case for the NIP-51 Grapevine WoT List. Two ways to do it:

1. Completely ignore zaps by npubs that are not on the list. 

or

2. Ascribe a weight to each zap, where the weight equals the Grapevine WoT Score of the zapper. Optional: make the weight an also function of the amount of the zap. Maybe weight = sats * Grapevine WoT Score.