Google has told Joy Hawkins that giving charitable donations in exchange for a positive review on your Google Business Profile listing is against its guidelines.
It would go specifically against the fake engagement policy that reads, "Paying, incentivizing or encouraging the posting of content that does not represent a genuine experience." A charitable donation would be considered "incentivizing" and thus against the rules.
Joy wrote, "In this case, the person leaving the review isn’t technically receiving the incentive since the money is going to a charity, but Google confirmed it is still against the guidelines. Although the user leaving the review technically isn’t getting the money, it can still lead to bias towards a positive review given the incentive of a donation. Ultimately, Google doesn’t want the customer experience to be swayed either way."
How does Google know this? That is a totally different story.
Forum discussion at Twitter.