What to trust
Location accuracy, Wi-Fi reliability and cleanliness are the three review dimensions for Japanese hotels that almost always track reality — complaints on these points tend to be genuine and consistent. Bed comfort is also reliable; it varies more than you'd expect even within budget categories.
What's mostly noise
Room size complaints from reviewers from the United States, Australia or Western Europe often reflect expectations calibrated to those countries' hotel norms rather than Japanese business hotel standards — 16-18 sqm rooms that Japanese reviewers rate fine will consistently read as 'tiny' to international guests. Worth discounting accordingly if that's the lens most reviews are written from.
Japan-specific quirks reviewers get wrong
The unit bath — a prefabricated single-moulded bathroom combining toilet, sink and tub — is standard and functional rather than a quality indicator; negative reviews of it as 'cramped' are describing the Japanese hotel norm, not a flaw in a specific property. Separately, the omiakase otoshi (mandatory small starter dish charged as a seating fee at izakaya) appears in restaurant reviews as a complaint about being 'charged for something I didn't order' — also standard practice, not a scam.