“I’m wondering if there is a standard practice that rabbonim suggest when it comes to reviewing products online….”
In the broader context, I suspect most rabbonim (and lawyers) would suggest avoiding online reviews entirely. As noted earlier, some merchants/service providers are incorporating provisions in their “small print” sales agreements which you routinely “agree to” prior to moving quickly to “checkout” that prohibits you from posting any negative or derogatory comments without first providing the merchant opportunity to correct the problem and even then, requiring you to go through arbitration. The practice is illegal in some states but still happens frequently for comments on Yelp, etc. where the ID of the reviewer is somehow obtained by the merchant