The hotel booking site HRS describes a 5-star hotel in Vienna as a "modern, elegant hotel," whose restaurant serves "selected seasonal products" and which also includes "a splendid classical café." On the photos, the hotel presents itself in the best possible light. Nothing negative is listed.

In the past, holiday makers had to rely on nothing other than these descriptions - and their own personal experiences. But in the day and age of the internet they can now read descriptions and reviews made by others. Sites like TripAdvisor, HolidayCheck, Zoover or HRS make it possible for users to rate providers.

By clicking through the user reviews of that same "modern, elegant hotel," you'll suddenly find out that it charges 35 euros ($39) a day for parking and that it doesn't provide free wifi access either. Another guest complains about dirty wallpaper and hairs in the bathroom.

What are your standards?

Reviews can allow travelers to get a real feel for the place, beyond the advertisers' spin. User ratings are therefore becoming increasingly important. "At this point we receive over 160 contributions a minute," Tom Breckwoldt from TripAdvisor told DW. "Altogether, there are over 250 million reviews and testimonies," he adds. These reviews are used by travelers very frequently.

According to Breckwoldt, some 96 percent of TripAdvisor users think the reviews by other travelers are very important when researching and booking a hotel. And this is the case beyond TripAdvisor: A survey by the University of Worms found that the majority of those questioned (90 percent) generally check reviews of hotels every time or at least most of the time, when booking a holiday.

Reviews can be very varied because everyone has their own standards and expectations when it comes to holidays. So while a stressed-out businessperson might welcome a holiday resort that offers a remote, peaceful location, a "party animal" might object to the isolated location and complain that the entertainment is boring, leading them to give the resort a bad review.

A survey by Tomorrow Focus, an internet social trend research company, showed that there are review portals in many areas, but that the focus on the travel sector is particularly high. Which begs the question: Why do users submit reviews in the first place? The survey found different types of reviewers: Most of them - some 45 percent - want to help others, while about 18 percent post their reviews to help places improve their service or to maintain good standards. Some 17 percent use the review to either praise a place or lodge a complaint.

Manipulation is a problem

Generally speaking, some 80 percent of reviews are positive, according to the study by Tomorrow Focus. This provides hotels free advertisement. But there is also a dark side. Not only do users' opinions differ, there is also a great risk of manipulation, as there is no legal requirement to use real names on the internet. So hotels might post bad reviews of their competitors, while at the same time, giving themselves good ones.

"Credibility is paramount, which is why TripAdvisor takes strong action against false reviews," Tom Breckwoldt says. "Given the size of the community, the number of fraudulent reviews is actually fairly low," he adds. Most fake reviews are spotted and blocked by TripAdvisor's security system.

Peter Gentsch, digital management and big data expert and founder of the Big Social Media company, is a little more pessimistic when it comes to the number of fraudulent reviews on these sites in general. "I would say the number of manipulated reviews must be around 20 or even 25 percent," he told DW. And these can have fatal consequences for the hotels: Good reviews can greatly increase the number of bookings, while bad ones can equally cause the business to crash.

A Munich pub and some student protest

The power of reviews in the tourism industry was recently demonstrated in Munich: Because of bad experiences with student fraternities, the pub manager of the Hofbräukeller decided to ban all student associations from his bar last summer.

The news spread quickly and those affected were upset about the ban. What followed was a storm of protests on social media. On Facebook, where some 700 satisfied customers had given the venue good ratings, the place slipped in a short space of time from being ranked with 5 stars to a mere 1.8, because there were suddenly over 3,000 bad reviews.

Even politicians got involved in the stand-off: Bavarian state Finance Minister Markus Söder, also responsible of the national Hofbräu brewery, which owns the pub, decided to lift the ban. Having been a member of a student fraternity himself, Söder would have therefore been technically banned from his own company. Once the ban was lifted, the students revoked or amended their bad reviews, and the rating of the Hofbräukeller has managed to climb back up to 3.3 again.