Make sure you report those messages. It's against Google's terms of service, and the Google Reviews product team genuinely wants to address those reports (at least that's what they've said in conversations with them)
I don't pay for advertising. I did that for my first 10 years in business. I have a Google profile but the only messages that I receive are offers for fake 5 star reviews. I am convinced that 99% of all 5 star reviews on Google are fake. I feel badly for anyone out there that is starting a business and believes that Google is a reliable source of new customers. I feel badly also for the people who search for a company and are scammed by companies with fake 5 star reviews.