What we're seeing when we look at some of these suspicious reviews is that there is no consistencies. People are all over the map, so that's something you may want to do when you're looking at reviews.
Are they reviewing mostly in same region or the same area, are they a local person that lives there, or are the reviews all over the place?
People do travel all the time obviously, but they should also have multiple reviews in one area. You can also check to see if reviews include details like specifics on products or services.