Hi @Molly42 , This topic has been discussed and discussed (I could say, ad nauseum) on the forum. Do a search using the spy glass for lots of thoughts and opinions on the subject.
For example:
https://forum.trustedhousesitters.com/t/when-a-potential-sit-has-past-sitters-but-no-reviews
https://forum.trustedhousesitters.com/t/sitters-reviews
https://forum.trustedhousesitters.com/t/what-would-you-do-if-last-4-5-sitters-didnt-review/
Fyi, unfortunately, the THS email app does not enable sitters to contact other sitters. (This has also been discussed.) You could ask these HO how it went with their last sitter. You could also go to the app and see if they have left a review for that sitter and judge from that. If they have left no review on the sitter’s profile, either the sit was a dud or it was canceled.