There is a fashion which has grown up as a result of web-based rating and review systems and it's not a pretty or pleasing fashion at all. Obviously the keyboard warrior is certainly older than the Internet, it's always been easier for a certain type of professional moaner to send a caustic letter rather than face their victim. But review bombing is a relatively new phenomenon. The concept seems relatively simple. A bunch of Internet trolls decide to target an individual business and using a host of bogus accounts set about writing derogatory and damaging reviews on every service which is appropriate for that business. Yell, Yahoo, Facebook, Trip Advisor etc. Whilst a number of these services have recently tightened up their systems and have made a commitment to remove obviously bogus or intentionally malicious reviews it is often too late in that the damage has already been done. It is also very difficult to implement if the trolls are reasonably intelligent and determined.
Some safeguards exist. Comment aggregation is one that the reading public should pay attention to before taking a very negative review at face value. If the author of the review has several entries on the same site it will always be useful to read a selection. If all reviews are extremely negative then it's safe to say this individual is embittered and probably not the most reliable reference. Slightly more concerning is if you find a host of negative reviews in a given geographic area and one shining recommendation. It's safe to assume on this occasion that the author has a vested interest and is far from unbiased....
A very unpleasant development of this trend are email to businesses demanding regular payments to prevent negative review being posted. There is an implied threat that if payment is not received, usually through Western Union, which is extremely difficult to trace, that these reviews will be placed and there is little the business can do to have them removed. Although illegal and very worrying these threats can usually be taken with a pinch of salt. Our unpleasant troll is looking for quick cash and is actually unlikely to follow their threat through. In doing so they would have to invest time and effort into a venture which would guarantee to net them nothing. Which is generally opposite to the characteristics of such individuals.
If you do happen across a flood of negative reviews about a business which has previously had a good reputation on-line, don't take these at face value. Try the place or product out. If you are satisfied with the product or service write a review or indeed, several reviews to that effect.
We can reverse the trend, if we take the time to give positive feedback.