If you are traveling, I think people generally like to know what they are getting themselves into before they arrive and this is especially true with backpacking since the low-cost aspect of the travel already kind of ensures you are going to be dealing with a slightly less than luxurious experience. This is part and parcel of backpacking and it is the price we pay for spending dramatically less than people who go on short holidays that are full-service, come with guarantees, and much higher levels of service.
In order to avoid the lemons, people will generally head to the internet in order to get some reviews or at least opinions about various places that exist on the tourism trail. Sadly, most of these sites are easily manipulated and you can't really trust what is being said by either the owners or even the people in the reviews.
Booking.com
Booking.com has emerges as one of the most popular booking sites among all price ranges, but in particular among the backpacking ones. At first glance the reviews section seems legit because it isn't possible to write a review about accommodation unless you booked into a place and the owner confirmed that you actually turned up and put it into the system.
The fallacy of this system was pointed out to me by a hostel owner years after he had sold his business and how easy it is to manipulate your overall score and even push genuine reviews to page 2 or 3. First, the owner sets up a bunch of fake accounts using throwaway emails like protonmail who have very lax signup requirements. Then the owner will make a bunch of extremely cheap rooms available and these rooms may not even exist as far as the consumer or Booking.com is concerned. Then the owner will book these rooms for a night knowing that the customers isn't actually going to stay in the room because neither the customer nor the room actually exist. If any real customers try to book the room the owner would simply decline the booking and approve all the bookings for the fake customers.
Then when the new customer "stays" there this fake account is entitled to write a glowing review giving 5 stars across the board. The owner of the place will suffer a small fee since Booking.com takes a 10% (it might be 15%) fee for all bookings made, but this particular owner was offering the fake rooms for $5 per night. This means he had to pay 50 cents for every 5 star review on his place. Is this a devious practice? Of course it is and it is widely used by hostels all over the world. Booking.com com doesn't care to address this because they are getting paid regardless.
Hostelworld
Hostelworld's review section was even easier to manipulate years ago, as you didn't even need to have stayed there in order to write a review, but rather you simply needed to respond to a email verification to attempt to keep the bots out.
When Hostelworld later adapted a review qualification just like Booking.com, the exact same thing started happening. The same owner of said hostel that I used as an example above told me that in addition to manipulating the system on your own companies based out of India who claimed to have hundreds of Hostelworld accounts would, for a fee give you as many 5-star reviews as you wanted. Unfortunately, they also had a feature to write negative reviews about any competing business that you choose.
Tripadvisor
These guys are the worst and unfortunately they are likely the most widely used.
The biggest problem with Tripadvisor is the fact that they have zero safeguards in place to ensure that you were actually ever there. As bad as Booking and Hostelworld are, their system is even worse. The only safeguards they have is that multiple reviews can not be made from the same IP address in rapid succession. Anyone with even a rudimentary understanding of VPN systems realizes how insanely easy this system is to circumvent.
There are some pretty funny stories out there about how some people spend a year making a non-existent restaurant the number one restaurant in London and another group that made a homeless shelter in Scotland one of the top ten hotels in Edinburgh.
Anyone who ever receives a negative review on Tripadvisor or simply wants to pump their numbers can go through the rigmarole of setting up 20 accounts or they can merely reach out to their pals on Facebook to write bogus reviews for their place. In one such instance I have to admit that a friend of mine with a tourism oriented business asked me to help him out and "write a review" for him but he had actually pre-written it for me because his SEO guy had given him particular keywords that would help his exposure.
So who can we trust?
Probably no one actually or you could look to FB groups of the city that you are going to be traveling in. You might not get the exact scoop using that method but at least you will have an army of fact checkers who are also members of the group so you have at least Some chance of getting the full story before deciding who to book with.
As far as established sites are concerned if I had to choose one I would probably go with Agoda.
While not perfect Agoda at least has the added benefit of doing a bit of verification of facilities before it goes live on their booking engine. They also require 100% prepayment and will flag certain things like "flash sales" where the owner make a $40 room $3 for 24 hours and will deny review-writing capabilities for these obviously fake promotions.
Basically, if someone wanted to scam the review section of Agoda it would cost them so much money that they probably wouldn't bother with it. The only downside is that Agoda doesn't generally feature the best value hostels since they do have a rather high lower-limit as far as how much a room can cost. Also, since the sign up process is so complicated with Agoda as far as being the owner of a business is concerned, many of the mom and pops simply decide to not have anything to do with Agoda.
It's shame that there are so many scammers in the world but that is just the way life is I guess. I would say that generally speaking, if you want to straight scoop about quality of accommodation, you are going to have to search a bit harder than the first page of a websearch because most of that, unfortunately, is likely tainted information.
Scam after scam. i know as i fell for some luxury hotel in New York and it was a total tip. I have learned that most hotels are actually cheaper if you book directly with them. They have specials that the other booking sites don't have and will also beat the price advertised on those sites.
someone I know who was the owner of a group of party hostels built up his FB friends list over a number of years like most of us do, then hit us up one by one to ask us to write reviews for his place. When I looked at all the reviews they all had the same "tone" to them, I believe that he authored hundreds of reviews and very few of them are genuine.
The bad news is that this deception totally works.
I would imagine that most tripadvisor listings that have a decent grasp on technology are likely riddled with fake reviews because like you said, if you don't cheat, the other guy is going to. The good news is that I dont' know many people that give much credit to tripadvisor anymore, it's just too easy to manipulate.