I share OP's skepticism of reviews on AirBnB given how predominant 5 star raves are. I can think of many plausible hypotheses for why this happens. Regardless of the reason(s) they got that way, the fact is that inflated reviews are close to worthless.
When browsing a property on AirBnB I look very closely at the owner's pictures, street maps, and Google Street View. Usually I also email the own to confirm details about the property, such as whether there's private access from the outside and whether all the "bedrooms" are fully enclosed by solid walls with proper doors! Probably about one-third of the time the owner never answers. Another one-third of the time the owner becomes hostile after even one such question. Ah, well. At least I'm weeding out the problem landlords in advance!