I believe that in the app interface you could have seen if these awful sitters had any sits where the HOs did not give a reference.
Unfortunately this is not the case. A HO’s profile will show the gap in reviews in the app, but a sitter’s profile will not. I only recently learned this even after being on THS for almost two years! Here’s a thread about it.
Edit to add:
There’s some confusion about it because a sitter can see the gaps on their own profile, but anyone else viewing their profile will not see the gaps.