This is my experience as well, as a Sitter…I pretty much “just know.” Most often our calls are more like a get-to-know you chat. The basic logistical questions get covered, but if the overall vibe is good/friendly and we have a few laughs during the convo, I generally feel that whatever else comes up can be worked out…and so far, so good. 
I was recommended by another HO with whom I am now friends. I visited the house and met the dog of the new member. She’d already joined and listed some dates before I was put in contact. She also has already filled the other dates that I couldn’t make. The only loser is THS, they won’t be getting any sit fees on this occasion. The mutual fiend is also a member but we don’t use THS for her dates, why would we? I think the new member is getting off to a great start, she’s had some help and suggestions from another HO and a sitter. How often does that happen? As for me, there’s no risk whatsoever. If the sit should be cancelled I’ll shrug my shoulders and carry on.
I’m doing as many sits as I can without using THS. I’m not a fan of vulture capitalism.