The best way to prevent bad reviews on Google My Business and other local business review sites is to provide your customer with the best quality of goods and services, and an excellent experience. If you've been doing this but are still getting bad reviews, it could be a competitor of yours or someone that has an axe to grind leaving fake reviews from different accounts.
Reputation management companies usually offer services to remove, and/or bury bad Google reviews.
Defamation Defenders does a great job at getting Google to remove negative reviews, and also at getting positive reviews for your business from authoritative Google accounts, which serves to push the bad review far down on the GMB profile.