I have a certain quasi-professional interest in online reviews, but since I have no results of interest to talk about, I’ll leave that for now. My current interest is in booking some accommodation in Ko Lanta (a Thai island) in mid November, and my current problem is that online hotel reviews are useless for mid-range accommodation.
All mid-range accommodation is rated between medium and poor on online review sites with lots of complaints about the quality of the rooms and the food. Most luxury accommodation is rated excellently, with praise of the rooms and the food. Gosh, that’s really useful: it turns out that mid-range accommodation is less luxurious than luxury accommodation. Using online reviews to make internal comparisons between accommodation in the same price range is basically impossible; unless you’re paying for the top 10% of accommodation by price in any given area, most of the reviews will say that where they stayed sucks and that the reviewer will never return. Compare guidebooks, where there will usually be some kind of overall summary of accommodation standards in the area and then their picks in each price range, so that if you follow their recommendations you at least in theory are getting better-than-the-odds accommodation for your chosen price range (before we take into account the effect that a popular guidebook recommendation has on availability, price and standards anyway).
I don’t know that there’s a professional/amateur distinction here, except as a side-effect. What’s really going on is whether the person is writing for themselves (to vent or boast about their choice in accommodation) or explicitly positioning their review so as to be helpful to other people. Most online travel sites have not managed to encourage people to write in such a way as to be helpful to other travellers. I’m not sure what would help; with accommodation it’s especially hard, because very few people will switch accommodation in a given location, so only professional or very dedicated amateur travel reviewers are able to say ‘given a budget of X, I’d stay in place Y over other options in this area.’ Wikitravel, for example, which was founded on the premise that ‘ordinary’ travellers (that is, people who aren’t dedicating their trip explicitly to write ups of the experience) can write as good or a better guidebook than people whose trip is entirely for the purpose of reviewing, has generally found that accommodation is a hard problem. In practice it’s mostly written by travel geeks, who are more likely to be couch surfers, and even if not, aren’t likely to stay in upper-mid and high end accommodation. I’m not surprised the ‘just tell us what you think!’ sites have trouble, but I’d like it if they were useful.