Getting reviews for your MAPS listing seems like a shot in the dark and frankly, due to human nature, people are more likely to go out of their way to post a bad review than a good one. I'm not sure if it's a vindictive reaction to bad service or if it just makes the individual feel better knowing he got even. In any case, there isn't much a business can do about a bad review.

The best strategy is to bury bad reviews with positive reviews. One way to do this is my requesting a review exchange with other local businesses. Most likely these business will already have a presence on Google MAPS making the process much easier. All they have to do is find your listing in MAPS and write a simple 5 start review. You of course do the same for them. Most business who have tried to manage Google MAPS rankings will understand the value of doing this.

Is it ethical? You bet it is! Honestly a business who doesn't believe you deserve a positive review probably won't do it! Nor should you even ask. So send a simple email to other local businesses, tell them you just submitted a positive review on their MAPS listing and would appreciate the same courtesy. I doubt you'll get much resistance and the results will be worth it.