Maybe even not blocking them outright but just rate-limiting would provide comparable friction. It could even be more effective if they never try the VPN route to discover that it's faster.
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.
With "wages low skilled" at 4650BDT [1] that's $55.50 at today's exchange rate. I'm standing by my estimate of "some", as a 2.7% "tax" on income isn't negligible, and could have far greater significance for those who earn at the bottom of the scale.
Because VPNs to American servers are dirt cheap.