If you limit the IP to the residential IP space then VPN costs become huge. You need some resident to rent his IP to you. If those residents get punished by the

If you limit the IP to the residential IP space then VPN costs become huge. You need some resident to rent his IP to you. If those residents get punished by their providers for that behaviour then soon you will have to rent apartments to buy your own connections. That's hundreds of dollars. Now, if Amazon would be sincere about preventing fraud, they would ban the IPs of fraudulent comments and somehow cooperate with the providers if they use random IPs. In other words, you would have to rent a new apartment for every bad review. That's an exhibitive cost.