It is not likely that there is a method that work perfectly, but there are steps that you can take that will help. If I find ANY reviews which are obviously faked I would be very unlikely to stay at the hotel. If they are prepared to lie to create a positive image, or need to do so, they are probably suspect in other areas as well.
When there are a range of hotels available in my price range I tend to look first at those with a substantial number of user reviews.
Fake reviews are usually short and stupidly positive. They are unlikely to contain major negative criticisms. They are unlikely to contain "mini stories" as some reviews do.
If reviews have been posted by people who claim to come from other countries I look for language which shows that the writer does not have language skills or styles which would be expected from a foreign writer. This usually is easy to spot and a clear indication.
Fake reviews often but not always come in batches. If reviews go something like
'OK Ok Poor Ok Bad Ok good good good OK Ok poor ...' I would guess that the run of "Good" assessments was possibly fake. They may not be, but then applying other tests helps check this.
If reports are VERY inconsistent between reviews I am suspicious. If some reviews say "dirty bedding, cockroaches, loud music, drugs sold in lounge, no food,grumpy staff, ..." and others say "clean, tidy, quiet, family atmosphere, polite staff ..." then I'd guess that one of the two sets of reports may be fake. Odds are that it's not the negative ones.
You can use a number of booking sites to check reviews, even if you do not book through them. If you have some specific hotels on a short list it does not take long to book them on other sites. If reviews are not consistent between sites, be suspicious. [I find Agoda is good for finding nearby hotels and checking approximate prices - they have a hover over map which shows hotels in an area and the alleged price shows when you hover over the hotel icon. Other sites can make price hard to check. ANY price is only a guide before all extras have been added.