TAM: I looked at your site and saw how reviews show. I don't do similar site(s) but I'll go through what I know about "filtering reviews" by review providers.
Large review sites certainly "filter reviews". I am not aware of any site trying to filter by assessing reviews by language to ascertain if it is faked. In the positive side, by owners/operators/employees. There could be an effort to try and filter reviews by the reviewers themselves.
Yelp filters reviews by people who aren't active reviewers/yelpers. Write only one or 2 yelp reviews and don't become active in the community with photos and other "yelp" activity "stuff" and the reviews are likely to be filtered. (they also filter for other reasons). They ostensibly filter for other reasons such as political reviews. Google certainly filters for seemingly too many reviews submitted in a short time period, as you have expressed concerns.
Google certainly has a filter on first time reviewers. I experienced it. They don't apply it like Yelp. Google has other technical filters; sending in reviews from a review station (ie similar to you identifying reviews by IP) using urls in reviews, supposedly no political reviews (they are not currently enforcing that) and other methods.
I am unaware of any large review site currently filtering for "repetitive language" or any language test to filter reviews. That doesn't mean its not in use anywhere, but simply that I am unaware of it. Years ago I had inside interaction with the google spam team. I asked about that issue and got a response that it was too difficult to do. At that time. The technology has undoubtedly improved, yet I am unaware of any site currently applying it.
I'd be careful in your personal assessment. We've accumulated well in excess of 1000 aggregate reviews on various sites. Years ago we ran into a problem with a competitor for one site. I'm sure they planted reviews. I was also sure at the time their "corpus" of reviews were all or virtually all internally created. The aggregate sum of their reviews at that time addressed EVERY single "hurdle" that consumers considered in purchasing the service. And no others. I submitted them with a list of industry hurdles to my inside contacts. (ha all the effort was turned down)
Later I reviewed the corpus of reviews. For whatever reasons they had lots more and they were seemingly more diverse. While considering the competitor's reviews I was simultaneously reviewing our existing corpus. I was convinced ours were clean and theirs were dirty. I submitted the two different review packages to some people that I considered independent. Their assessments were different than mine. I suppose I was looking at these with too critical of an eye.
Beware of that in your assessments.
Only a small percentage of users of a service will submit reviews even if being asked by the service provider....possibly in the ranges of 4-20%, and probably skewing on the lower side. That being the case, review writers are not authors or generally overwhelmingly literate. In fact some are downright illiterate. But they may really appreciate the service provider.
It is not unusual for a review writer to submit the exact same word for word review to more than one site (copy and paste). This of course might present problems with regard to duplicate content and other issues. Some folks try and work around it by taking screen shots of reviews and applying them to their sites. That is a way to appease the review writer and get the review on the site while simultaneously providing acknowledgement that the review can be found elsewhere.
The sites that carry reviews make and enforce policies that support their economics. Specifically that means that even while review spam is significant and possibly growing and not shrinking the review providers don't want to put too many staff hours to reading and review filtering by human staff. I would suggest that is a good business policy.
I didn't read the terms and conditions on your site about submitting reviews. In light of how difficult it is to obtain reviews for these types of businesses I wouldn't necessarily refrain from duplicate reviews on other sites (such as facebook). I would state that they need to make you aware that they are copies. Hey that is okay if its a real reviewer and not a submission from the owner; at least in my eyes, if not all others. Then I would present the review as a screen shot or with attribution to the original source or both.
BTW: I searched in google for pet boarders Cornwall UK. I think I saw 27 listed. One had 25 google reviews, 1 had 18, 1 with 12, 1 with 7 and the rest had 3 or less with a large percentage having none. I think this reinforces how difficult it is for these businesses to get reviews at all. It also suggests the boarders with with 18 and 25 might have an aggressive review "management" or review collection policy in place (if they aren't faking reviews). I'm not aware of other review aggregators...except your site.
Readers LIKE and LOVE reviews. You might want to highlight the aggregate volume of reviews on your site. It attracts readers/visitors.
Hey if you find automated review filter mechanisms let me know. I'm interested in knowing what is out there.