a client asked me how to leave anonymous reviews on google and i handled it badly

this is the part of doing sites for local businesses that nobody warns you about. the owner of a takeaway i built for asked me over a coffee how to leave anonymous reviews on google, because the place that opened across the road was eating his lunch trade and he wanted to leave a few one stars under names nobody would recognise. he did not think he was asking me for anything wrong. in his head it was even, because he was sure the other place had done it to him first, and he might be right, he got three one stars in the first week they were open. i said no, badly. i went straight into the lecture, told him it was fraud, told him google can see the device, and he went quiet and payed for the coffee and we did not speak for about two weeks. what i should have led with is the practical thing, that it does not work and it is a stupid risk for a man with a lease. there is no anonymous. the display name can be anything you like, sure, but the account behind it has a phone number and a device and a location history, and google clusters all of that. a batch of fresh one stars on one buisness from accounts that all touched the same wifi is exactly the pattern the spam system exists for. best case nothing happens. worse case his own listing gets flaged, and the listing is where his friday night orders come from, so he would be betting the actual business on knocking 0.1 off somebody else's average. the other thing i should have said is that the review that would hurt his rival most is the one he could never fake anyway, a real customer of theirs writing that the food arrived cold. we ended up fine. he messaged me a month later to say his rating had gone to 4.7 because he started asking people, and did i want to come in for something. i still think about how much better that converstaion would have gone if i had led with the risk instead of the morals. do you tell a client straight out that it is fraud, or do you just make it sound like too much hassle to be worth doing?