Google added a new guideline to their review snippet documentation about fake and undisclosed incentivized reviews, and here it is:

> • Don't include fake or undisclosed incentivized reviews on your page or in your structured data markup. Examples include:

> ◦ Reviews that aren't based on a genuine experience of a product or service

> ◦ Reviews written in exchange for a benefit (such as money, discounts, vouchers, or free products) that don't clearly and prominently disclose the incentivization