Zap just means sending bitcoin via lightning network from onr nostr account ( a npub) to another. So if a person create 5 accounts, he/she can zap account 2 from account 1, then zap account 3 from account 2, then back to account 1,etc. so zapping is fake not from 2 real people. 1 person can create 1 million account to follow an account and zap that account. So it can be extremely fake. But if the website/ nostr clients charges a cut for each zap, this will discourage fake zaps, but not entirely as a rich person can accept to pay for a charge.