I heard recently from a friend that another person in business that they know often write or ask friends/family to write reviews on review sites for them.
They cheat.
Simple as that.
If you are loading your reviews up on sites like Yelp or TripAdvisor you are cheating the system. People want to read real reviews, not trumped up happy thoughts from your Aunt Alice.
What do you do then when you have multiple or even just one negative review on a site? First listen to the review. Is your customer service not as great as it should be? Are you not serving your clients as well as you could? Did the soup that day turn out how you wanted it to? If you aren't doing your best, make real changes. Respond the review, invite them back, tell them you changed.
If you think the reviewer was just crabby or you were just having a bad day, chalk it up to that. Respond nicely in the comments and move on. There is no reason to have it removed unless it is particularly vicious or just totally inaccurate.
These sites are built to make the consumer make better choices, but they can also be used to make your business better at what it does. Listen to the criticism and find the areas of improvement. Don't short cut. It won't help you or anyone else, and trust me, you will find yourself getting more of those bad reviews. Clean it up and get on track! See it as a way to get real feedback - not a reason to balk.