I'm floored that Steve doesn't realize people love to complain, and that giving people an outlet to moan about their bad apartment is all the incentive they need.
If you want to remove the information asymmetry, you need a random sample of previous tenants. This is hard to get unless you force people to write reviews or provide some incentive that is stronger than their urge to complain.
But that's not the point with this site. As an apartment hunter (probably from another city or state), you have little information on structural problems with the apartment. How can you find out if your 1st-floor apartment floods or lacks concrete foundation? Your realtor or landlord probably won't tell you the truth.
So, instead, you can turn to former tenants. This site isn't a review data aggregator--it's a tool for reaching informational equilibrium.
This is entirely explained by game theory. If you think the final star rating for something should be something other than what the average currently is, you maximize your power over the rating by using only 1 or 5 star ratings.
To me, it looks like a self-selection issue: people only review a product if it either (a) changes their life positively, or (b) causes them trouble. If a product only impacts someone's life in a trivial way, well, why write a 3-star review for a trivially good product?
Agree with random samples. Also need larger samples. Or something like a carfax for apartments.
Example: there's an apartment near where I live which looks like a great deal on paper, but on some internet review site there were lots of complaints about how there are hidden fees for things like parking, and how the apartments aren't insulated so you end up with a huge heating bill. I didn't see those complaints with other apartments, so I think they're legit.